In 2014 the US Surgeon General issued a call to action for the prevention of skin cancer in the American population. Specifically, the focus of the call to action was the reduction of exposure to ultraviolet radiation (UVR), as this is the most preventable risk factor for developing skin cancer [1
]. At the time of the Surgeon General’s call, 76,665 people in the United States were diagnosed with melanoma and 9234 people died as a result of this cancer. In the USA, melanoma ranks as the fifth most prevalent cancer among men and sixth among women [2
]. The incidence of melanoma in non-Hispanic whites has increased significantly from 2005 to 2014. Although incidence rates have increased for people from ages 15 to 44 years, the rates also have increased for people aged 55 years and older [3
]. Globally, the incidence of melanoma in 2015 was 351,880, with an age-standardized rate of five cases occurring per 100,000 persons [4
]. Older men that reside in the Australasian, North American, and European regions experience the greatest burden for melanoma [4
Melanoma is caused by severe intermittent sun exposure, sunburn, or use of tanning beds [5
]. Occupational sun exposure and total lifetime sun exposure also are associated with melanoma risk in people living at low latitudes [7
]. Although some sun exposure may be accidental or inadvertent, some people seek sun exposure to obtain a suntan. Additionally, some people use UV tanning beds to obtain a suntan, and this can increase melanoma risks. Young women (aged 14–30 years) typically have been at the most risk for melanoma from tanning beds [8
]. Laws in the United States and Canada have increasingly required either parental consent or the meeting of minimal age requirements to use a tanning bed [9
]. Although this has led to a decrease in tanning bed use among young women, people still seek a tan through sun exposure [9
Intermittent sun exposure and severe sun exposure (or overexposure) leading to sunburn typically occur during the warmer summer months when solar radiation is the most intense, and when warmer ambient air temperatures permit outdoor recreational activities, often as people expose greater areas of skin (e.g., hiking, swimming, tennis, etc.) [11
]. Some occupations also have intermittent sun exposure, such as teachers on playground duty [12
]. Some lower latitude locations are so warm during the summer that this may contribute to a decrease in the amount of time that most people spend outside, and the sun protection measures that they use [13
Anecdotally, the authors have observed that people vary in the seasons that they experience risks for sunburn according to their subjective heat preferences, and how this relates to their being outside. Here, thermal perceptions refer to the individual differences that exist in the interpretation and preference for a given thermal environment. Such individual differences in heat perception and preference are part of behavioral thermoregulation, where people try to balance comfort, health, and the performance of work or recreational tasks by their behavioral choices of environments [14
Beyond these observations, two studies have suggested that people who dislike heat and hot conditions may experience heightened risks for sunburn the during spring and fall months when milder ambient air temperatures afford relief from summertime heating during recreational activities [8
]. In this regard, objectively-based measures such as temperature, heat balance models, or the recently derived Universal Thermal Comfort Index (UTCI) may not fully explain a person’s likelihood of being outside and getting a sunburn [15
]. In addition to seasonal considerations, the individual variability in sun exposure as it relates to temperature and thermal comfort suggests that individuals may differ in the extent which they dislike or prefer being in warm or hot outdoor environments [17
]. The implication for sun exposure and skin cancer prevention is that those who like heat and hot conditions may experience greater risks for sunburn during the summer months. Further, people who dislike heat and hot conditions may experience greater sunburn risks during the spring and fall, but less during the summer. This reasoning is supported by research that found that peoples’ perceptions of solar radiation (sun sensation) contributed the most to their thermal sensations in outdoor spaces [21
Individual differences in heat perception and preferences for thermal environments exist for several reasons. First, people may differ in the thermal environments to which they are acclimatized [14
]. People from subtropical and tropical locations are acclimatized to higher temperatures compared to people from mid- and high-latitude regions. Importantly, culture and environmental attitudes have been observed to affect thermal perceptions of comfortable temperatures [20
]. Second, the existing biometeorological indices of thermal comfort have been developed around average values for variables such as body surface area, body weight, percentage of body fat, skin wittedness, and cardiac output, among other things [22
]. The use of average anthropometric values in models of thermal comfort suggests that the individual variability in perceived heat may not be accounted for. In addition, models of heat stress have been challenged in predicting individual observed sweating rates, and thus the rate at which a person may regulate cooling [22
]. Third, and relatedly, an essential component in models of human thermal comfort is the individual metabolic rate [14
]. Averages of metabolism are frequently used in thermal models, yet the metabolic rate can be quite variable and can depend upon one’s level of physical fitness and thyroid functioning, among other things [14
Finally, existing thermal comfort models have not included higher-order psychological processes such as significant past experiences of temperature extremes, attitudes, beliefs, and the contributions of mood and emotion [17
]. Some people may not feel or experience the degree of heat and the associated discomfort that has been normatively associated with a given biometeorological index. Further, it is possible that if they experience the heat and their body’s response to it (e. g., intense perspiration), they are not bothered by this or and do not negatively evaluate the environment as too warm or too hot. Alternatively, other people prefer cooler or milder temperatures for outside activities and also may believe (erroneously) that this temperature regime is associated with fewer risks for sunburn [15
]. In this article, we report the results of a study of the relationships of subjective heat perceptions and preferences with the use of sun exposure precautions. We adopted the perspective of Knez and colleagues that personal and psychological variables may exert an important role along with weather, place, and time (here, months of the year) in affecting peoples’ sun protection behaviors [25
Our experiences and this review of the literature suggested three hypotheses to us, the first of which was that people would differ individually in their subjective preferences for warm/hot environments. Some people will exhibit an affinity for heat while others will not. Second, we hypothesized that people with a higher level of dislike for heat and hot conditions would pursue sun exposure experiences less frequently or to a lesser extent than people who prefer warm conditions. Third, we expected that peoples’ perceptions and preferences for heat would affect when during the year that they may be more susceptible to sun over-exposure. Specifically, people who dislike heat and hot conditions may be at risk for sun over exposure during the early spring and later fall months when ambient air temperatures are less warm. Conversely, people who express an affinity for warm or hot outside conditions may experience greater risks for over exposure during the entire warm/hot season of summer.
We found that people possessed individual perceptions about both their thermal environments and how their bodies respond to such conditions. These perceptions also give rise to preferences (liking or disliking) for heat or hot outside environments. As such, the items of our survey constitute a measure of attitudes about hot outside conditions [20
]. Moreover, the 15 items in the survey exhibited a high internal consistency and suggested that, taken together, they provide a useful indication for the extent to which people disliked heat or hot conditions. To our knowledge this represents the first study of its kind to assess heat attitudes, especially a dislike for hot outside conditions, and to relate them to UVR exposure and to taking precautions against sun (UVR) over-exposure and hence skin cancer prevention.
We also observed that people differed individually in their disliking of heat. Although the distribution of scores deviated from that of a standard normal distribution, the sample of participants exhibited a wide range of heat-related preferences, with most exhibiting a moderate degree of dislike of hot conditions. We attempted to understand the source of the score non-normality by examining the score distributions separately by gender and race. This did not produce any significant improvements in the degree of fit with a normal distribution. One possible explanation for the score distribution that we observed stems from the fact the research site was located within a subtropical humid climatic region [27
]. Sampling a region that has a more balanced climatic year with winters that are as cold as the summers are hot may yield a more normal distribution of scores with respect to dislike of hot conditions.
Perhaps most importantly, the results of this project showed that there were statistically significant relationships of dislike of heat and hot conditions with both past tanning behavior and in the times of year that people preferred to be outside. The dislike of heat and hot conditions shared from 7% of the variability with suntanning in the previous year to 14% of the variability in peoples’ attitudes towards obtaining a suntan. These results were noteworthy because they related to choices people made, or may make, about UVR exposure, simply because they perceived ambient thermal conditions to be aversive. For people with a higher dislike of heat, the risks for UVR overexposure are minimized at the outset because they tend to avoid or minimize sun exposure. At the opposing end of the continuum, once people choose to suntan, issues regarding the use of sunscreen, hats, and protective clothing become much more salient in avoiding sunburn.
Suntanning behavior pertains to deliberate efforts to darken the skin due to sun exposure. However, what about more general exposure to UVR when outdoors during different months and seasons? We discovered that people had very different monthly UVR exposure profiles according to their individual dislike of heat. In this study, the respondents who disliked heat experienced more risks for overexposure in April, May, and October—more people were outside in these months than those who used sun protective measures, potentially due to the local climatic conditions at that time. The group of respondents who did not express a dislike of hot conditions evidenced a much wider interval of months in which they enjoyed being outside—from April through to October. It was only in the summer seasons (June, July, and August) that a higher proportion of people in this group tended to use sun protection than those who enjoyed being outside.
The authors are pursuing two lines of further research based upon the results that we reported here. First, we are interested in understanding what might contribute to individual differences in subjective thermal perception. We have designed another study in which we will examine the contributions of: 1. the climate in which one developed as a child and adolescent, 2. the person’s physical activity levels and physical fitness level, 3. body mass, 4. basal metabolic rates, and 5. levels of thyroid hormone. These variables may together explain some of the individual differences we observed here in thermal perceptions [14
]. Second, we want to explore the sunburn risk perceptions and how these may be related to a like or dislike of warm or hot thermal environments [20
This study was limited in that it relied upon participant self-reports to assess all of the variables. Additionally, the study design was cross-sectional. Another limitation pertains to the demography of the sample, who resided in a lower latitude climate of the southeastern United States. The survey responses of people who reside in cooler, higher latitude regions with a long winter and a short summer may well differ from those of the participants in the present sample. Finally, because we were interested in peoples’ subjective perceptions of thermal environments, we did not assess at this exploratory phase the contributions of physical variables such as body mass or activity levels. Our work is limited in this way; however, we will examine those contributions in a subsequent study.
Despite these limitations, the study was unique both in assessing attitudes on hot thermal conditions and sun exposure, and in documenting that individual differences existed. Our emphasis on individual attitudes and sun exposure preferences may help to explain a small but unique portion of the variability in individuals’ risk behaviors for melanoma that are not currently accounted for by approaches that use objective variables such as temperature, heat balance models, thermal comfort indices, or UV indices [17
]. In this regard, our approach is responsive to the recent call for novel and interdisciplinary approaches to understand and reduce melanoma risks [33