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Review

What’s New in Heat-Related Illnesses of Travel: Narrative Critical Appraisal and Summary of the Updated Guidelines from the Wilderness Medical Society

1
Faculty of Dentistry, University of Toronto, Toronto, ON M5G 1G6, Canada
2
Department of Medicine, Division of Emergency Medicine, McMaster University, Hamilton, ON L8L 2X2, Canada
3
Division of Infectious Diseases, Department of Medicine, University of Toronto, Toronto, ON M5S 3H2, Canada
4
Department of Biology, McMaster University, Hamilton, ON L8S 4K1, Canada
5
School of Medicine, Oregon Health Sciences University, Portland, OR 97239-3098, USA
6
Institute of Medical Science, University of Toronto, Toronto, ON M5S 3G9, Canada
7
School of Medicine, Royal College of Surgeons in Ireland, D02 YN77 Dublin 2, Ireland
8
Department of Medicine, University of Toronto, Toronto, ON M5S 3H2, Canada
9
Tropical Disease Unit, Toronto General Hospital, 200 Elizabeth Street, 13NU1350, Toronto, ON M5G 2C4, Canada
*
Author to whom correspondence should be addressed.
Climate 2026, 14(5), 106; https://doi.org/10.3390/cli14050106
Submission received: 25 March 2026 / Revised: 6 May 2026 / Accepted: 13 May 2026 / Published: 16 May 2026

Abstract

Rising planetary temperatures and extreme heat events have led to an increased incidence of heat-related illnesses, such as heat stroke, globally. Widespread adoption of measures to prevent and treat heat-related illnesses is an increasingly urgent issue given the rising global temperatures; promotion of such evidence-based strategies is needed to reduce heat-related morbidity and mortality globally. Such heat-related environmental illnesses are differentially experienced by those without access to ambient cooling and those engaged in outdoor work and recreation. Moreover, the adverse impacts of heat-related illness experienced by residents of the Global South necessitates the inclusion of high-quality recommendations around prevention and treatment into clinical and public health practice in order to address health equity and human rights considerations. The current guidance on prevention strategies and therapeutic interventions for heat-related illness has been iterated and published by the Wilderness Medical Society (WMS). In this critical appraisal, we have summarized the evidence-based guidelines and highlighted the updated recommendations that reflect evolving issues in heat illness research. Application of the Appraisal of Guidelines for Research and Evaluation (AGREE) II framework has enabled a quality assessment of the guidelines to be performed, which we present herein. The adoption of evidence-based practices around heat-related illness has the potential to reduce morbidity and mortality and improve global population-level health in light of the warming climate.

1. Introduction

Increasing rates of adventure travel coupled with a warming climate inherently places individuals maladapted to heat at risk of heat-related illness [1]. Heat-related illness encompasses a range of clinical conditions in the T67 category of ICD-10 codes, including but not limited to the following: heatstroke and sunstroke (T67.0), heat syncope (T67.1), heat cramps (T67.2), and heat exhaustion (T67.3. T67.4, T67.5). Healthcare professionals must be attuned to and develop expertise in illnesses arising from environmental interactions and extremities of climate. Such clinical competency requires that practitioners are up to date on the evidence-based treatments of climate- and environmental-related illnesses; they must also develop knowledge of how to preventatively reduce risk and treat resulting illnesses. Updated guidance from the Wilderness Medicine Society (WMS) has been published around the prevention and treatment of acute altitude sickness [2], frostbite [3], heat illness [4], and avalanche and non-avalanche snow burial [5]. We herein summarize the heat-related illness practice guidelines4 and their corresponding evidence grading and provide a critical appraisal of the guidance provided.
The widespread adoption of measures to prevent and treat heat-related illnesses is an increasingly urgent clinical and public health issue given rising temperatures globally, and promotion as well as critique of such evidence-based strategies is needed to reduce heat-related morbidity and mortality; this is particularly the case in the areas that are most vulnerable to extreme climatologic events, such as the Global South, where mitigation and counter-measures may be unavailable due to resource constraints. The adoption of such strategies also aligns with the principles of health equity and human rights given the additional vulnerabilities of infants and children, pregnant people, the elderly, and those with disabilities, both physical and neuropsychiatric, to heat-related illness. This evidence appraisal is intended to update and guide physicians providing care to patients in any part of the world who are at risk of travel-related heat illness, including physicians practicing emergency medicine, critical care, travel and tropical medicine, pediatrics, occupational medicine, and primary care.

2. Summary of Guidance and Narrative Critical Appraisal Methodology

The practice guidelines and focus on research advancement for heat-related illness systematic reviews were summarized, with emphasis on updated literature presented in the 2024 iteration of the WMS guidelines [4]. The heat-related illness systematic review with updated guidelines [4] was assessed for the quality of evidence that gave rise to each practice recommendation noted in the WMS guidelines. Two authors used “The Appraisal of Guidelines for Research and Evaluation (AGREE) II” instrument to evaluate methodological rigor and transparency in guideline development [6,7]. A six-domain, 23-item checklist scored from 1 to 7 on a scale across items within each domain comprises the AGREE II instrument [6,7]. Step-by-step instructions on how to independently apply and score the instrument are available in the User’s Manual at www.agreetrust.org, to which the authors adhered. Scores of 1 suggest ‘strong disagreement’ with fulfillment of domain criteria while scores of 7 indicate ‘strong agreement’ with domain criteria fulfillment and quality of reporting. Scores between 2 and 6 are assigned when domain criteria are not fully met, with scores increasing when more criteria are fulfilled. As such, the use of the AGREE II framework requires a high degree of subjective judgment. Scaled scores—both composite and aggregate—in the six AGREE II domains are available in Supplementary Table S1. Prevention interventions featured in the WMS guidance publication [4] are provided in Table 1 and therapeutic interventions with the associated WMS guidelines-derived recommendations are synthesized and appraised in the text. The authors of the WMS guidance document used the American College of Chest Physicians (ACCP) updated classification scheme for recommendations in clinical guidelines, considering risks and benefits balanced against burden of evidence, which enabled them to assign both a grading of the quality of evidence and a strength of their recommendation.

3. Narrative Critical Appraisal Results

3.1. Application of AGREE II [6,7] Criteria in Methodological Rigor and Transparency Appraisal

AGREE II Domain 1: Scope and Practice. The aggregate and scaled scores in this domain were 6.3/7 and 89%, respectively (Supplementary Table S1). The inference of the target population and evaluated interventions was enabled through the methodological detail provided. However, clear “PICO” (population–intervention–comparator–outcome) questions were unavailable in the guidelines. Therefore, it is unclear whether both adult and pediatric patients were within the scope of the guidelines. The objectives of the guidelines are clear and transparent.
AGREE II Domain 2: Stakeholder Involvement. Aggregate and scaled scores for this domain were lowest—at 4/7 and 50%, respectively—due to an absence of clear involvement of patients or the public in the guideline development (Supplementary Table S1). Moreover, only some relevant stakeholder medical specialties were represented, with apparent absence of representatives from pharmacology, allied and paramedical services, pediatrics, and pediatric subspecialties including pediatric ICU physicians. This second domain could be enhanced through clarification of the intended audience and greater exposition around methods of engagement.
AGREE II Domain 3: Rigor of Development. The aggregate and scaled scores for this domain were 5.6/7 and 77%, respectively (Supplementary Table S1). A systematic and transparent approach to evidence synthesis was undertaken, and the strengths and limitations of the evidence base are described. The formulation of recommendations according to the quality of underlying evidence and strength followed a clear and rigorous process. Each intervention was weighed according to its risks and benefits, following the American College of Chest Physicians (ACCP) updated classification scheme for recommendations in clinical guidelines. The guidance document was also peer-reviewed. However, it is unclear if data specific to the behavior of self-pacing—that is, the behavior of slowing the work rate in response to perceived heat stress—was considered for the prevention-related recommendations. The presence of two prior iterations of the guidance suggests that there is a plan to update the guidelines although there is no specific text describing that process or how often it would occur.
AGREE II Domain 4: Clarity of Presentation. The aggregate and scaled scores for this domain were high at 6.8/7 and 98%, respectively (Supplementary Table S1). The recommendations are easily located in the guidance document and are written with clarity and lack of ambiguity.
AGREE II Domain 5: Applicability. The aggregate and scaled scores for this domain were on the lower side—5.9/7 and 81%, respectively—as attention to implementation barriers and adoption strategies across intended stakeholder groups could not be discerned (Supplementary Table S1). There was limited content around how more detailed information about barriers and facilitators in practical scenarios and clinical care was sought, and how this might have influenced the guidelines. The benchmarks are explicit and underpinned by quantitative biological and physiological metrics, amenable to auditing of practice, although no description of the process to undertake such monitoring is stated.
AGREE II Domain 6: Editorial Independence. The highest aggregate and scaled scores were achieved for this domain at 7/7 and 100%, respectively. There is an absence of funder influence and influence of those with competing interests (Supplementary Table S1).
The application of the AGREE II instrument led to an overall guidance quality rating of 5.5/7 with a scaled score of 75%. The guidelines should be recommended for implementation accordingly (Supplementary Table S1).

3.2. Highlights of Heat Illness in the Guidelines: Definitions and Epidemiology

Heat illness can affect a wide variety of people, from elite athletes who participate in endurance races to attendees at music festivals who spend long hours in the sun with limited water access. Particular immutable demographic vulnerabilities to heat-related illness include extremes of age (both infants and young children as well as the elderly), pregnancy, physical and neuropsychiatric or cognitive disability, as well as chronic cardiorespiratory conditions. In the US, mortality from heat illness is greatest among persons aged 65 years and over at 0.7 per 100,000 population [8]. With climate change, there has been an increasing frequency of heatwaves, which are defined as an “unusual period of hot weather over a region persisting for at least two consecutive days during the hot period of the year” [9]. According to the Centre for Disease Control, from 1 January to 31 December 2023, “a total of 119,605 emergency department visits” related to heat illness were recorded [8]. Given the threat that heatwaves pose to human health, it is especially important to be able to quickly identify and appropriately treat heat illness. There is a wide spectrum of clinical heat-illness presentations from minor illnesses, such as muscle cramps and lightheadedness, to life-threatening heat stroke. Table 2 outlines the different categories of heat-related illness along with corresponding ICD-10 codes. Hyperthermia, or an increase in the body’s normal physiologic setpoint, is correlated to the severity of heat illness. However, while temperature thresholds alone may indicate risk, they are non-diagnostic and should not be used routinely in asymptomatic individuals; this was demonstrated by two studies which found 15–56% of asymptomatic runners have a core temperature > 40 °C and 11% have a core temperature > 42 °C [10,11]. Such data support that inclusion of clinical data is required to improve the specificity of definitions in heat-related illnesses such as hyperthermia, the severity of which is governed by the duration and extent of thermal stress [4]. In the US, it has also been shown that extreme heat exposure often exacerbates chronic underlying medical diagnoses such as hypertension and cardiovascular disease [12]. Heatwaves also magnify the effects of other common ecological phenomena, which may have region-to-region variance globally, such as wildfires—which liberate particulate matter into the air-, drought conditions—which threaten access to water and portend risk of flooding when rains occur, e.g., cyclones, “urban heat islands”, and reduced air quality. In particular, ground-level ozone conditions (i.e., “smog”) can form quickly during heatwaves and imperil lung capacity through oxidant effects on alveoli and bronchiole, thereby posing a significant risk to cardiorespiratory function especially in those with underlying lung disease such as asthma. Furthermore, the reported rate of heat-related mortality tends to be higher among persons living in rural and urban core counties [12]. More broadly, it is advisable for all healthcare facilities and public health units to maintain knowledge of regions with a high risk of seasonal, regular heatwave events in order to advise travelers to prepare appropriately [9]. Travelers themselves need to be aware of the aforementioned regional ecophenomena that might portend increased risk of heat-related illness.

3.3. Highlights of Heat Illness in the Guidelines: Strategies for Prevention

Although heat illness is an incidental occurrence, many factors should be considered with regard to its prevention. There are two types of acclimatization to heat stress on the body: behavioral and physiological. The updated 2024 WMS guideline recommendations include those pertaining to both types of acclimatization including activity, clothing, and weather that lower the risk of heat-related illness (Table 1). For one, heat accumulation of all activities can be acknowledged by considering factors such as the activity intensity and duration as well as the frequency of rest periods that prevent an individual from overheating. Outdoor activities should be planned with careful consideration of the thermal strain on an individual, as represented by the “wet-bulb globe temperature index”, which is a standardized measure of environmental heat stress that accounts for multiple factors including “air temperature, wind speed, humidity, and solar radiation” [4,13]. The heat index, which is a measure of the contribution that “high temperature and high humidity” imperil a person’s ability to cool themself, can be used as a second line metric to assess for risk [4]. Alao, appropriate clothing and equipment for a given activity must be identified by considering methods for optimizing heat exchange and heat protection. Previous WMS-recommended prevention strategies remain intact and include the following: enhancing overall aerobic fitness, heat acclimatization through one to two hours daily of activity in heat exposed environment for at least 7 days, and adequate hydration through a “drink-to-thirst” approach which aims to prevent more than 2% body loss of water. Evidence surrounding the use of osmotic agents to increase physiologic water absorption is limited and primarily studied in high-performance athletes [14]. The benefits of pre-cooling are likely limited to short durations of heat exposure during exertion [4].
As with previous iterations of such guidelines, the 2024 WMS update includes recommendations relating to health and medications which affect risk of heat-related illness (Table 1). General screening for certain pre-existing medical conditions that are associated with increased susceptibility of heat illness is recommended. These include hypohydrosis, extensive scars, diminished cardiopulmonary reserve due to aging, and high body mass index, as suggested by a large prospective study among military recruits [15]. A previous history of heat injury is also a risk factor for recurrence of heat illness [4]. Several prescription and non-prescription medications and toxins, including alcohol, amphetamines and other stimulants such as cocaine, beta blockers, and antipsychotics may impair thermoregulation or lead to increased heat production; as such, their use should be limited, where possible, to mitigate risk [16].

3.4. Highlights of Heat Illness in the Guidelines: Interventions for Treatment

Treatment of heat injuries can be categorized largely into field treatments and hospital treatments. Both categories tend to follow the simple algorithm of removal from heat, then airway and circulation stabilization, followed by on-site rapid cooling until body temperature is reduced to 102.2 °F or 39 °C, and transport to the hospital to rule out end organ dysfunction. Specific treatment strategies are dictated by availability of resources and severity of illness [4].
Identification of the disease severity is guided by measuring body temperature, of which the most reliable is rectal temperature measurement, followed by esophageal (WMS 2024: strong recommendation, moderate-quality evidence) [17,18]. For mild cases, specifically exertional muscle cramping, management centers around oral hydration with isotonic salt or electrolyte fluid replacement (WMS 2024: strong recommendation, moderate-quality evidence). Of note, oral rehydration has been shown to be equally effective to intravenous rehydration in these cases [4]. Compression stockings can be considered in relieving heat edema. Moderate cases such as heat syncope are managed by removing the patient from heat, supine positioning or with legs above heart level, and oral hydration. More severe cases of heat illness, specifically heat stroke, may require more invasive treatments, including the following: intravenous rehydration using 1 to 2 L (or 20 mL/kg in pediatric patients) of isotonic crystalloids (WMS 2024: strong recommendation, low-quality evidence), cold water immersion (WMS 2024: strong recommendation, high-quality evidence), and evaporative cooling (WMS 2024: strong recommendation, low-quality evidence). “Cold water immersion therapy” is identified as the most optimal field treatment for temperature reduction, with multiple studies on young and healthy patients showing a 0% fatality rate using this method [19]. Extrapolation of results such field trials to persons of greater age and/or comorbidity requires further investigation. It ideally involves immersion of the entire body into cold or ice water. In situations where such intervention is not feasible, cooling can be achieved with immersion into the coldest available water source (WMS 2024: strong recommendation, low-quality evidence) [4,20,21,22]. The application of ice packs in the axilla, groin, and neck should be avoided (WMS 2024: strong recommendation, moderate-quality evidence) [10,23]. However, recent evidence supporting the use of ice-sheets (i.e., bedsheets “soaked in ice water”) where cold-water immersion is unavailable has emerged and demonstrated acceptable efficacy for cooling in exertional heat stroke [24,25,26].
Evaporative cooling, which involves dousing the patient with cool water followed by fanning, has shown to possess half the cooling rate of immersion cooling; as such, it is considered an adjunct cooling method or can be used when cold water immersion is unavailable (WMS 2024: strong recommendation, low-quality evidence) [27]. In the past, evaporative cooling combined with convection was primarily used in elderly patients suspected of non-exertional heat illness; however, ice water immersion is now considered first-line therapy in this patient population.
In field circumstances where a patient is presenting with altered level of consciousness and the clinical suspicion for hyperthermia (regardless of degree) is strong, it is recommended to empirically initiate active cooling, even if core temperature is unknown or measured below the conventional “diagnostic threshold of 40 °C” (WMS 2024: strong recommendation, moderate-quality evidence) [4]. It is recommended that field treatment of patients sustaining heat injuries are followed up by more comprehensive health check-ups in healthcare settings to monitor any after-effects of the heat injury, such as electrocardiographic changes, and confirmatory blood tests for internal organ functioning (e.g., creatinine and liver enzyme) as outlined by multiple case reports [28,29]. Updated WMS guidelines also advise that patients with heat syncope or individuals at risk for heat syncope always take caution prior to participating in strenuous exercise, and to seek cardiology diagnostics after a syncopal episode (WMS 2024: weak recommendation, low-quality evidence).
Laboratory trials and empiric data supporting both field and in-hospital use of body bags for performing cold-water immersion have emerged as an effective and resource efficient way achieve rapid cooling [30,31]. In a case study by Kim and colleagues, an altered elderly patient was cooled from 40 °C to 38.4 °C in ten minutes by an ice and water filled mortuary bag (i.e., “body bag”) [30]. She rapidly returned to a normal level of consciousness and was discharged straight from the emergency department. Other in-hospital treatment strategies such as cold intravenous fluids or cooling blankets can be used as adjunctive but are not effective as a primary cooling method. More invasive therapies, including body-cavity lavage with old isotonic fluids and endovascular cooling are not recommended as first line cooling therapies. Target cooling temperatures should range between 38.3 °C and 38.8 °C—at this point, the body is able to thermoregulate safely (WMS 2024: strong recommendation, moderate-quality evidence). Shivering and agitation may occur in a heat stroke patient, and management with benzodiazepines or opiates can be considered (WMS 2024: strong recommendation, high-quality evidence) [4]. Further, shivering has not been observed clinically to slow the cooling process and in fact, is observed less frequently in the comorbid, obtunded patient. Lastly, antipyretics—which target the hypothalamic set-point—should be avoided as they are ineffectual in treating exercise-induced heat illnesses, which arise due to an individual’s failure to cool in the face of heat stress (WMS 2024: strong recommendation, moderate-quality evidence). Other pharmacological treatments such as dantrolene are rarely considered effective in treating heat stroke (WMS 2024: strong recommendation, moderate-quality evidence), especially when treating severe cases, as a randomized controlled trial of dantrolene versus placebo found no significant difference in cooling rates [32].
Heat injuries can be classified in many ways, and the WMS guidelines have outlined evidence-based guidelines on their prevention and treatment, as based on exercise-induced hyperthermia mimicking heat illness conditions.

4. Discussion

Heat-related illnesses is an ever-increasing urgent clinical and public health threat given rising temperatures globally, and adoption of evidence-based preventive and therapeutic strategies is needed now more than ever. Promotion as well as critique of such evidence-based strategies is also needed to best inform clinical practice and reduce heat-related morbidity and mortality, particularly in areas most vulnerable to extreme climatologic events, such as in the Global South. The WMS has updated their guidelines on heat-related illness, for which a summary around prevention can be found in Table 1.
In addition to prevention and treatment, the updated WMS guidelines have also expanded on areas of potential further research, which would primarily involve developing sound and ethical methodology to better replicate heat illness physiology for the purpose of conducting clinical trials. Also, it would be worthwhile to delve into cooling methods such as endovascular catheters and other hospital-based systems as part of heat illness treatment in critically ill patients. Aside from the future areas of research outlined by WMS, the guidelines may also benefit from further exploring the downstream clinical aspects of heat-related illness to reflect increasing clinical concerns of medical professionals, such as effects of heatwave events on health, and their influence on vector-borne diseases, as well as the clinical impact of air pollution and humidity on travelers [7]. Limitations of the guidelines in their current form are few and relate to imprecision around the specific PICO-formatted questions being addressed. Therefore, uncertainty remains around whether or not pediatric issues in heat-related illness have been fully interrogated and considered during the guidance development process. Moreover, differential impacts of heat-related illness according to PROGRESS+ factors [33,34], including but not limited to age, pregnancy status, socioeconomic status, occupation, and place of residence (including the precarity of their housing) warrant greater exposition from a health equity and human rights perspective. ‘Travelers’ encompass a highly mobile populace and include persons traveling for mass gathering sporting events [35], religious pilgrimages [35], skilled and manual labor, medical care, and visiting friends and relatives, all of which portend risks of heat-related illness that differ from those incurred by average tourist travelers from high-income countries. Additionally, inclusion of the full search strategy with literature cutoff date, even as a Supplementary File, would be helpful to the reader and would improve accessibility of the guidelines. It is unclear from the guidelines if data specific to self-pacing—that is, the behavioral measure of slowing the work rate in response to perceived heat stress—was specifically considered for the prevention-related recommendations, although some degree of self-pacing is implicit in the recommendations around acclimatization to heat, optimization of physical fitness, and optimization of rest periods. Involvement of additional stakeholders including patients affected by heat-related illness, members of the public, pediatricians, public health experts, and allied health professionals, particularly first responders, would enhance the subsequent iteration of the guidelines. Clarity around the exact process and timing of any guideline updates could be considered. Also, the guidelines could benefit from additional exposition around barriers and facilitators to stakeholder adoption. As noted previously, resource-constrained regions of the global South are differentially affected by heat at both population and individual levels, and travelers to such destinations may be unaware that interventions available in their home country may be unavailable locally. Feasibility barriers in low–middle-income regions relate to the resources—including personnel, equipment, and infrastructure—needed for interventions such as cold-water immersion (compared to evaporative cooling, for example), medical evacuation and high-level monitoring, and both field and acute care training requirements. Indeed, according to the World Health Organization, “research is needed on temporary, low-impact and low-cost cooling options deployable at scale” in order to improve equitable access to heat illness prevention [35].
The strengths of the guidelines include clear recommendations lacking in ambiguity that are easily identified throughout. A highly rigorous process with standardized approaches was used to evaluate the quality of the literature systematically reviewed in the guidelines4 in order to assign a “strength of recommendations” throughout, which were also free of competing interests.

5. Conclusions

The WMS developed updated guidance on prevention and treatment of heat-related illness in 2024. These guidelines, which have been reviewed and narratively appraised herein based on their level of quality, transparency, and evidentiary support according to the risk to benefit ratio for each recommendation produced in the guidelines, serve as a systematically derived evidence-based approach to heat-related illness that also provide biological benchmarks for monitoring outcomes. The guidelines were developed in a systematic and rigorous manner and scored highly according to AGREE II criteria. The WMS guidance document also underscores the need for expanded research efforts to close knowledge gaps within the field of climate and heat-related medical science, a sentiment that was reiterated recently by the World Health Organization [35]. Such concerted efforts can expand the scope of evidence-based practice in global public health and ideally standardize implementation of recommendations within medical and organizational practices. Communication of evidence-based strategies to prevent and treat heat-related illnesses is an ever-urgent clinical and public health issue of global concern. Given the differential impact of extreme climatologic events related to global warming on vulnerable persons living in the Global South, widespread adoption of such preventive and therapeutic strategies is a matter of health equity and human rights. By critiquing and appraising the synthesized evidence highlighted in the WMS guidelines, we aim to raise awareness and underscore the importance of incorporating such interventions into clinical and public health practice.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/cli14050106/s1, Table S1: Appraisal of updated WMS Guidelines for the Prevention and Treatment of Heat Illness using the AGREE II framework.

Author Contributions

A.O., F.J., M.M., D.K., M.P., N.P.D., O.E.—literature review and synthesis, drafting the manuscript, and critical revision of the manuscript; G.D.H.—literature review and synthesis, critical appraisal, drafting the manuscript, and critical revision of the manuscript; A.K.B.—conception of report; literature review and synthesis, critical appraisal, drafting the manuscript, critical revision of the manuscript, and; overall project oversight. All authors have read and agreed to the published version of the manuscript.

Funding

Dr. Boggild is supported as a Clinician Scientist by the Departments of Medicine at the University of Toronto and the University Health Network.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

All data are presented in the manuscript.

Conflicts of Interest

Dr. Boggild oversees the Tropical Disease Fund for Excellence at the University Health Network Foundation, which has received a generous unrestricted educational grant from Seegene Canada. Neither Seegene nor UHN had any role in the development of this manuscript or influenced its content. The authors declare that they have no conflicts of interest.

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Table 1. Summary of WMS Heat Illness guidelines [4] updated in 2024 with appraisal of evidence for preventive interventions evaluated through systematic review.
Table 1. Summary of WMS Heat Illness guidelines [4] updated in 2024 with appraisal of evidence for preventive interventions evaluated through systematic review.
Heat-Related Illness
Recommendation [4]
Reported [4] Evidence StrengthReported [4] Evidence QualityComments
INDIVIDUAL FACTORS
Screen for pre-existing medical conditionsStrongModerateIncludes elevated body mass index (BMI)
Consider a personal medical history of heat injuryStrongLowAs a risk factor for recurrence
Avoid medications—both prescription and non-prescription—that could impair thermoregulationStrongLowExample: neuroleptics, antipsychotics, beta-blockers, amphetamines and other stimulants (e.g., cocaine), alcohol
Optimize aerobic fitness prior to heat exposureStrongModerate
Engage in one to two hours per day of
heat-exposed exertion for at least one week
StrongLowFor acclimatization to hot environment
Ensure normal hydration status prior to exertionStrongModerate
Adopt a “drink-to-thirst” approach to fluid replacement during heat exertionStrongModerateTo replace fluids and avoid >2% loss of body weight
ENVIRONMENTAL FACTORS
The wet-bulb globe temperature index (WGBT) is preferred method of establishing riskStrongHighHeat index is the second-line risk establishment metric
ACTIVITY FACTORS
Modify environment and remove gear during periods of rest and breaksStrongLowOptimize duration of rest and opportunities for cooling during rest periods
CLOTHING AND EQUIPMENT
Select clothing and equipment that can: isolate the body from the heat source and optimize heat lossesStrongLowEvaporative, conductive, convective, and radiative mechanisms of heat loss should be optimized
Table 2. Categories of heat illness and their relative severity.
Table 2. Categories of heat illness and their relative severity.
Condition and ICD-10 CodesDefinitionRelative Severity
Heat edema (ICD-10 T67.7)“Dependent extremity swelling due to interstitial fluid pooling.” Mild
Exertional muscle cramps, heat related (ICD-10 T67.2)“Exercise-associated painful involuntary muscle contractions during or immediately after exercise.”
Heat syncope (ICD-10 T67.1)“Transient loss of consciousness with spontaneous” recovery associated with heat exposure.Medium
Heat exhaustion (ICD-10 T67.3 [anhydrotic], T67.4 [salt depletion], T67.5 [unspecified])“Heat illness due to exposure to high environmental heat or strenuous exercise; signs and symptoms include intense thirst, weakness, discomfort, anxiety, dizziness, syncope; core temperature may be normal or slightly elevated >37 °C (98.6 °F) but <40.5 °C (105 °F).”
Heat stroke (ICD-10 T67.0)“Heat illness characterized by a core temperature > 40.5 °C (105 °F) and central nervous system abnormalities such as altered mental status, seizure, or coma.” Causes can be categorized into “passive exposure to environmental heat (classic heat stroke) or strenuous exercise (exertional heat stroke).”Severe
This table has been reproduced and slightly altered with permission from Elsevier (License No. 4854431488855).
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Omidi, A.; Jazuli, F.; Hawley, G.D.; Meconnen, M.; Kain, D.; Polemidiotis, M.; Do, N.P.; Egbewumi, O.; Boggild, A.K. What’s New in Heat-Related Illnesses of Travel: Narrative Critical Appraisal and Summary of the Updated Guidelines from the Wilderness Medical Society. Climate 2026, 14, 106. https://doi.org/10.3390/cli14050106

AMA Style

Omidi A, Jazuli F, Hawley GD, Meconnen M, Kain D, Polemidiotis M, Do NP, Egbewumi O, Boggild AK. What’s New in Heat-Related Illnesses of Travel: Narrative Critical Appraisal and Summary of the Updated Guidelines from the Wilderness Medical Society. Climate. 2026; 14(5):106. https://doi.org/10.3390/cli14050106

Chicago/Turabian Style

Omidi, Arghavan, Farah Jazuli, Gregory D. Hawley, Milca Meconnen, Dylan Kain, Mark Polemidiotis, Nam Phuong Do, Olamide Egbewumi, and Andrea K. Boggild. 2026. "What’s New in Heat-Related Illnesses of Travel: Narrative Critical Appraisal and Summary of the Updated Guidelines from the Wilderness Medical Society" Climate 14, no. 5: 106. https://doi.org/10.3390/cli14050106

APA Style

Omidi, A., Jazuli, F., Hawley, G. D., Meconnen, M., Kain, D., Polemidiotis, M., Do, N. P., Egbewumi, O., & Boggild, A. K. (2026). What’s New in Heat-Related Illnesses of Travel: Narrative Critical Appraisal and Summary of the Updated Guidelines from the Wilderness Medical Society. Climate, 14(5), 106. https://doi.org/10.3390/cli14050106

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