Consumer Awareness of Microbial Contamination and Identification of Key Pathogenic Bacteria in Lip Cosmetic Testers

Abstract

Background: With the increasing popularity and diversification of cosmetic products, an expanding number of retail stores are providing in-store testers to allow consumers to try products before purchasing. However, growing concerns have been raised about microbial contamination and the associated risk of infection due to the shared use of these testers. This study aimed to investigate consumer awareness and perceived susceptibility to microbial infection associated with the use of lip cosmetic testers, and to identify major pathogenic bacteria, thereby offering evidence to support the need for improved hygiene management practices. Methods: The survey examined the use of lip cosmetic testers and related side effects, as well as perceptions of product hygiene and microbial contamination. Awareness of microbial infection and consumer sensitivity to product safety were measured using a five-point Likert scale. Microorganisms were detected through PCR analysis of genomic DNA. Results: Among 134 respondents, 95% had previously used lip cosmetic testers, and 90% recognized the potential for microbial contamination. Sensitivity to product safety was not significantly associated with sociodemographic factors. However, susceptibility to microbial infection from tester use was significantly higher among participants of older age and with higher education levels. PCR analysis of lip cosmetic testers revealed frequent detection of Staphylococcus epidermidis and Pseudomonas aeruginosa. Other detected bacteria included Streptococcus oralis, Streptococcus salivarius, Streptococcus pneumoniae, and Escherichia coli, all of which are known to cause oral and respiratory infections. Conclusions: The analysis revealed that the majority of individuals who have used lip cosmetic testers expressed a high level of concern regarding product contamination and the potential for infection. Multiple pathogenic bacteria linked to oral and respiratory diseases were identified in the opened tester products. These findings underscore the necessity of establishing regulatory guidelines for the management of lip cosmetic testers and highlight the importance of enhancing consumer awareness regarding hygiene practices.

1. Introduction

Cosmetic consumers tend to prefer trying products directly before making a purchase, rather than relying solely on product information. The increasing prevalence of cosmetic specialty stores offering individual product testers reflects marketing strategies and distribution trends shaped by this consumer behavior [1]. As of 2024, the global K-beauty product market is estimated to be worth approximately USD 14.69 billion (approximately KRW 19.7 trillion), with projections indicating growth to about USD 31.82 billion (approximately KRW 42.6 trillion) by 2033 [2,3]. The Asia-Pacific region, in particular, represents the largest market for K-beauty products, accounting for approximately 35% of the global share [2]. Lip color cosmetics exhibit differences in color payoff depending on the individual, leading consumers to apply testers directly to the lips or skin to evaluate color and texture. This practice raises serious hygiene concerns due to potential microbial contamination. In 2017, the Korea Consumer Agency conducted microbial testing on 42 tester products collected from 16 cosmetic retail stores, targeting four types of microorganisms: total aerobic bacteria count, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa [4]. The results showed that 33.3% of the products, including eyeshadows and lip testers, exceeded safety thresholds for harmful microbes. Among the 16 lip products tested, four (25%) exceeded the standard for total aerobic bacteria, and S. aureus was detected in three products (18.8%). Foreign substances and residue were visually identified on some items. In a 2017 case from California, USA, a woman filed a lawsuit claiming she contracted oral herpes (HSV-1) after using a lipstick tester at a Sephora store [5]. While official data confirming the presence of the virus in the lipstick was lacking, herpes simplex virus (HSV-1) is known to potentially survive for several hours in moist environments such as lipstick. This anecdotal report is significant as it publicly raised concerns about the microbial transmission risks associated with shared tester products through consumer experiences. After originating from oral lesions, HSV was found to remain viable for approximately 2 h on skin, 3 h on clothing, and up to 4 h on plastic surfaces [6].

Unlike general cosmetic products, lip cosmetics such as lipstick, lip gloss, lip tint, and lip balm, are applied directly to the lips and may enter the body through oral exposure. Due to their frequent direct application to the lips or hands, lip cosmetic testers are highly susceptible to contamination by various microorganisms, such as herpes simplex viruses and staphylococci, as they are repeatedly used by unspecified consumers. The lips are composed of mucosal tissue, making them more susceptible to microbial infiltration than keratinized skin. Due to their high moisture and lipid content, lip cosmetics create an ideal environment for bacterial proliferation and may increase the risk of oral and respiratory infections [7]. When lip cosmetic testers are significantly contaminated with bacteria or contain pathogenic microorganisms that may lead to oral and respiratory infections, increasing consumer awareness of infection risks and enforcing stricter hygiene measures in retail environments become imperative. Nevertheless, research reports addressing consumers awareness of contamination and infection risks associated with cosmetic testers remain scarce. Moreover, opened products such as testers are not currently regulated by specific microbial limit standards, and comprehensive investigations into microbial contamination are very limited [8].

This study aims to evaluate consumers’ hygiene-related perceptions of lip cosmetic testers available in retail stores and to identify key bacterial species linked to oral and respiratory infections. The findings intend to offer evidence supporting the necessity for infection control measures and the establishment of effective hygiene management strategies for these testers. For this purpose, a survey was conducted to evaluate consumers’ hygiene-related perceptions of lip cosmetic testers, and bacterial detection was performed focusing on pathogenic microorganisms that must be absent under cosmetic safety regulations, as well as bacteria implicated in oral and respiratory diseases.

2. Materials and Methods

2.1. Ethical Considerations

This study was reviewed and approved by the Institutional Review Board of Eulji University (IRB No. EU24-84). All procedures were conducted in accordance with the ethical standards outlined in the Declaration of Helsinki. Informed consent was obtained electronically from all participants prior to data collection.

2.2. Survey

This study targeted adult women aged 20 years and older residing in Seoul and Gyeonggi Province, South Korea (Mean age: 38.2 ± 15.8 years). Data were collected over a three-week period beginning on 18 March 2025, using a self-administered online questionnaire. The survey was distributed via online platforms, and all participants were provided with detailed information about the purpose of the study in advance. A total of 138 individuals participated in the survey; after excluding four cases with incomplete responses on key variables, data from 134 respondents were included in the final analysis. The minimum required sample size was estimated using G*Power 3.1.9 software (Heinrich Heine University Düsseldorf, Düsseldorf, NRW, Germany). Based on the chi-square distribution for cross-tabulation, with a medium effect size (Cohen’s f = 0.25), a significance level (α) of 0.05, and a statistical power (1–β) of 0.80, the required sample size was calculated to be 133 participants. The questionnaire consisted of items on general characteristics, usage experience and adverse effects of lip cosmetic testers, hygiene perceptions regarding tester products, and perceptions of microbial contamination. Perceptions of microbial infection risk and consumer sensitivity to product hygiene were measured using a five-point Likert scale.

2.3. Collection of Lip Cosmetic Testers

A total of 30 opened lip cosmetic testers (experimental group), consisting of lipsticks (n = 12), balm-type products (n = 9), and lip tints (n = 9), were collected from specialty cosmetic stores. All testers had been opened within one month prior to collection. These samples were collected in December 2024. An additional 30 unopened products of the same types and brands were collected as the control group.

2.4. Bacterial Culture

To culture bacteria contaminating the collected lip cosmetic testers, the lip-contact surfaces of each product were evenly streaked onto 100 mm Tryptic Soy Agar (TSA) plates (Becton, Dickinson and Company, Sparks, MD, USA). All streaking procedures were conducted on a UV-irradiated clean bench. The plates were incubated under aerobic conditions at 37 °C for 36 h in a laboratory incubator. Visible bacterial colonies were harvested from the culture plates using a sterile scraper and used for DNA extraction for subsequent polymerase chain reaction (PCR) analysis. To prevent drying of the agar plate surface during incubation, sterile water–containing plates were placed inside the incubator. For the negative control, TSA plates without bacterial inoculation were incubated under the same conditions for the same duration.

2.5. Genomic DNA Extraction and Polymerase Chain Reaction (PCR) Analysis

Bacterial DNA was extracted from the cultured samples using the ExiPrep™ Plus Bacteria Genomic DNA Kit (Bioneer, Daejeon, Republic of Korea) in accordance with the manufacturer’s protocol. The concentration and purity of the extracted genomic DNA were measured using a spectrophotometer at 260 nm and 280 nm (Nanodrop 2000, ND-2000; Thermo Fisher Scientific, Inc., Waltham, MA, USA). Specific gene targets for the detection of major risk-associated bacteria related to oral and respiratory diseases were selected based on previous literature, and primers were designed using the PrimerQuest Tool (Integrated DNA Technologies, Inc., Coralville, IA, USA) [9,10,11,12,13,14,15,16]. A total of eight bacterial species were targeted, with 16S rRNA included as an internal control. PCR amplification was conducted using the AccuPower^® PCR Master Mix (Bioneer) according to the manufacturer’s instructions. The reactions were performed on a SimpliAmp Thermal Cycler (Thermo Fisher Scientific, Waltham, MA, USA) under the following thermal cycling conditions: initial denaturation at 95 °C for 30 s, annealing at 56–60 °C for 30 s, and extension at 72 °C for 30 s, repeated for 30 cycles. PCR products were subjected to electrophoresis in a 1.2–1.5% agarose gel containing ethidium bromide at 50 V for 30 min. The presence of the expected PCR amplicons was confirmed using a UV transilluminator (Bio-Rad Lab, Hercules, CA, USA).

2.6. Statistical Analysis

The primary variables in this study were categorical, and descriptive statistics were presented as frequencies and percentages. For items with subcategories, the denominators used for percentage calculations were specified. To assess participants’ sensitivity to microbial infection and perceived safety regarding lip cosmetic testers—both measured through multiple questionnaire items—exploratory factor analysis (EFA) and reliability testing were conducted. EFA with Varimax rotation was employed to extract principal components by grouping variables with high correlations, which were then used in subsequent analyses. The number of components was determined based on commonly accepted statistical guidelines: eigenvalues greater than 1.0 [17], interpretation of the scree plot [18], and factor loadings of 0.50 or higher. The reliability of the extracted components was evaluated using Cronbach’s alpha coefficient. For the second stage of analysis, group differences in perceptions were examined according to sociodemographic characteristics. Since the Shapiro–Wilk test indicated a violation of normality, non-parametric methods (Mann–Whitney U test and Kruskal–Wallis test) were used to assess statistical significance. All data processing and statistical analyses were performed using Microsoft Excel and R version 4.3.2 (R Core Team, R Foundation for Statistical Computing, Vienna, Austria), with a significance level set at 0.05.

3. Results

3.1. Characteristics of the Survey Participants

A total of 134 individuals responded to the survey. Among them, the largest age group was 20–29 years (58.21%, n = 78), followed by those aged 50 and above (26.12%, n = 35) and 30–49 years (15.67%, n = 21). Unmarried participants accounted for 64.18% (n = 86), and over 80% (n = 108) of respondents had attained a college degree or higher. Approximately 53% (n = 71) of respondents were economically active (

Table 1. Demographic Characteristics of the Survey Participants.

Question	N	%
Age group (years)
20–29	78	58.21
30–49	21	15.67
>50	35	26.12
Marital status
Single	86	64.18
Married	47	35.07
Other	1	0.75
Education level
High school graduate or less	26	19.4
Currently attending college	56	41.79
Bachelor’s degree or higher	52	38.81
Employment status
Yes (employed or on temporary leave)	71	52.99
No (not economically active or seeking employment)	63	47.01

All values are presented as n (%) for categorical variables.

).

3.2. Usage Patterns and Perceived Contamination of Lip Cosmetic Testers

Among the 134 respondents, approximately 95% (n = 127) reported having used lip cosmetic testers (

Table 2. Survey on Awareness of Lip Cosmetic Tester Use and Product Contamination.

Question	N	%
I have used lip cosmetic testers (n = 134)
Yes	127	94.78
No	7	5.22
What is your usual method of using lip cosmetic testers? (n = 127)
Direct application to lips	19	14.96
Application to lips using a disposable tool	9	7.09
Application to lips using fingers	16	12.6
Swatching on the back of the hand	81	63.78
Other	2	1.57
What is your purpose for using lip cosmetic testers? (Multiple responses allowed, n = 127)
To check the color and pigmentation	120	94.49
To assess texture and usability	69	54.33
To check for allergic reactions	2	1.57
To evaluate the taste and scent	6	4.72
To assess overall quality	4	3.15
Other	-	-
Have you ever experienced adverse effects after using a lip cosmetic tester? (n = 127)
Yes	5	3.94
No	122	96.06
Do you think lip cosmetic testers can be contaminated with microorganisms? (n = 134)
Yes	120	89.55
No	3	2.24
I don’t know	11	8.21
Specify the reason for your perception of microbial contamination (Multiple responses allowed, n = 120)
Experienced an expired or contaminated product	15	12.5
Because many people use it	106	88.33
Contamination due to saliva	69	57.5
Contamination from contact with hands or skin	47	39.17
Contamination due to exposure to dust or other particles	37	30.83

All values are presented as n (%) for categorical variables.

). The most common application areas were the back of the hand (63.8%) and the lips (14.96%) for color testing. The primary purposes of using testers were to “check the color and pigmentation” (94.5%) and to “assess texture and usability” (54.3%). About 4% of those with tester experience reported having experienced adverse effects. Regarding contamination, approximately 90% (n = 120) of all respondents perceived that lip cosmetic testers could be contaminated by microorganisms. The most frequently cited reasons were “because many people use them” (88.33%), “contamination by saliva” (57.5%), “contact with hands or skin” (39.17%), “exposure to dust and dirt” (30.83%), and “direct experience of product deterioration” (12.5%).

3.3. Analysis of Microbial Infection Susceptibility and Product Safety Sensitivity Toward Lip Cosmetic Testers by Participant Characteristics

To assess participants’ microbial infection susceptibility and product safety sensitivity toward lip cosmetic testers, an exploratory factor analysis (EFA) with reliability assessment was conducted. The analysis included four items related to perceptions of microbial infection risks and three items related to consumer sensitivity toward lip cosmetic product safety. Based on statistical criteria for factor loadings and the conceptual relevance of the items, two factors were extracted: Factor 1, labeled ‘Susceptibility to microbial infections’, and Factor 2, labeled ‘Consumer sensitivity regarding product safety’. The reliability coefficients (Cronbach’s alpha) for the two factors were 0.751 and 0.729, respectively, indicating that the constructs were appropriately extracted to represent awareness of microbial infection risk and consumer sensitivity to product safety in the context of lip cosmetic testers (

Table 3. Exploratory analysis of susceptibility to microbial contamination in lip cosmetic testers (Factor 1) and sensitivity to product safety (Factor 2), and reliability of the measurement instrument.

Question	Factor 1	Factor 2	Cronbach’s α
Susceptibility to microorganism
I am aware of the effects of microorganisms on oral health.	0.853	−0.038	0.751
I generally have an interest in microorganisms.	0.765	−0.058
I tend to be concerned about microbial infection when using lip cosmetic testers	0.713	−0.204
I tend to be concerned about side effects when using lip cosmetic testers	0.649	−0.199
Consumer sensitivity regarding product safety
I usually pay attention to the ingredients and contents listed on lip cosmetics.	0.181	0.929	0.729
I usually pay attention to the preservatives and allergy-related information indicated on lip cosmetics.	0.007	0.918
I usually pay attention to the expiration date on lip cosmetics.	0.309	0.569
Eigen value		2.115		2.370
Kaiser–Meyer–Olkin (KMO) = 0.586, Bartlett’ test of sphericity = 401.206 (p < 0.001)

Bold and italicized values indicate the factor loadings used for calculating Cronbach’s α.

). The Kaiser–Meyer–Olkin (KMO) measure of sampling adequacy was 0.586, indicating a borderline level of suitability for factor analysis. However, Bartlett’s test of sphericity (χ² = 401.206, p < 0.001) confirmed that the correlations among variables were statistically significant, thereby supporting the appropriateness of conducting factor analysis; consequently, an exploratory factor analysis (EFA) was carried out. According to the results based on the two extracted factors, age and education level were significantly associated with susceptibility to microbial infection (

Table 4. Differences in perception according to sociodemographic factors.

		Susceptibility to Microorganism			Consumer Sensitivity Regarding Product Safety
		Mean	SD	p-Value	Mean	SD	p-Value
Age group
	20–29 years	3.52	0.78	0.004	1.97	0.79	0.128
	30–49 years	3.69	0.72		2.3	0.89
	50 years and older	3.09	0.7		2.3	0.88
Marital status
	Single	3.45	0.782	0.79	2.18	0.88	0.241
	Married	3.4	0.761		1.97	0.77
Education level
	High school graduate or less	2.96	0.74	0.001	2.31	0.85	0.306
	Currently attending college	3.47	0.69		2.07	0.83
	Bachelor’s degree or higher	3.63	0.79		2.04	0.86
Employment status
	Yes (employed or on temporary leave)	3.37	0.803	0.268	2.14	0.86	0.82
	No (not economically active or seeking employment)	3.5	0.736		2.07	0.82

p-values were calculated by Mann–Whitney U test and Kruskal–Wallis test for non-normality distribution using Shapiro–Wilk test. Bold and italicized values indicate statistical significance.

). However, none of the demographic characteristics showed a significant association with consumer sensitivity to product safety.

3.4. Detection of Bacterial Contamination in Lip Cosmetic Testers

Bacterial cultures were performed on the surfaces of 30 opened and 30 unopened lip cosmetic tester products. The forward and reverse primer sequences targeting specific bacterial species are listed in

Table 5. PCR primers, detection targets, and amplification conditions for the target genes used to detect each bacterium.

Target Bacterium	Primer (5′→3′)	Target Gene	PCR Product Size (bp)	Annealing Temp.(°C)
16S rRNA [9]	F-5′-CCT ACG GGN GGC WGC AG-3′ R-5′-GAC TAC HVG GGT ATC TAA TCC-3′	16S V3–V4	460	55
E. coli [10]	F-5′-TGG TAA TTA CCG ACG AAA ACG GC-3′ R-5′-ACG CGT GGT TAC AGT CTT GCG-3′	uidA	147	60
P. aeruginosa [11]	F-5′-ATG GAA ATG CTG AAA TTC GGC-3′ R-5′-CTT CTT CAG CTC GAC GCG ACG-3′	oprL	504	60
S. salivarius [12]	F-5′-ACA ACT GAA ACC TTT GCA TCT GG-3′ R-5′-CGG TCG CAT CTG TAC GGT AA-3′	gdh	278	60
S. oralis [12]	F-5′-CCT TGG GAG CAA GGA ATA TTT TGA ATC TG-3′ R-5′-AGA GCG ATA TTG ACC ACG AAT AAA C-3′	SO3	732	60
S. pneumoniae [13]	F-5′-ACG CAA TCT AGC AGA TGA AGC A-3′ R-5′-TCG TGC GTT TTA ATT CCA GCT-3′	lytA	101	60
S. aureus [14]	F-5′-GCG ATT GAT GGT GAT ACG GTT-3′ R-5′-AGC CAA GCC TTG ACG AAC TAA AGC-3′	nuc	279	60
S. epidermidis [15]	F-5′-TAT GGT GGT GTG ACG GTG AC-3′ R-5′-CGT TGA TGG TGT TGT TGA AC-3′	tuf	370	60
S. mutans [16]	F-5′-CGG AGT GCT TTT TAC AAG TGC TGG-3′ R-5′-AAC CAC GGC CAG CAA ACC CTT TAT-3′	gtfB	750	60

. PCR analysis revealed that no bacterial growth was observed in any of the unopened control products. However, among the 30 opened products (experimental group), bacterial growth was observed in 18 samples (60%) (Figure 1A). Genomic DNA was extracted from the cultured bacteria, and PCR was conducted to detect eight target bacterial species (Figure 1B). Among the contaminated products, Streptococcus epidermidis and Pseudomonas aeruginosa were the most frequently detected, found in 17 out of 18 positive samples (94.4%). Staphylococcus aureus and Streptococcus mutans were each detected in 12 samples (66.7%). In addition, Streptococcus oralis (8 samples, 44.5%), Streptococcus salivarius (7 samples, 38.9%), Streptococcus pneumoniae (4 samples, 22.2%), and Escherichia coli (1 sample, 5.6%) were also identified (

Table 6. Detection results for eight types of bacteria identified in the opened lip cosmetic testers.

Bacterial Strain	No. Detection (n = 18)	Detection Rate (%)
S. epidermidis	17	94.4
S. pneumoniae	4	22.2
S. aureus	12	66.7
P. aeruginosa	17	94.4
S. salivarius	7	38.9
S. mutans	12	66.7
S. oralis	8	44.5
E. coli	1	5.6

).

4. Discussion

The aim of this study is to investigate consumers’ hygiene-related perceptions regarding lip cosmetic testers and to detect major pathogenic bacteria associated with oral and respiratory diseases, thereby providing evidence supporting the need for infection control during tester use. Cosmetics have evolved beyond simple beauty tools into means of self-expression and social identity, with consumer demand continuing to rise [19]. Many consumers prefer to test cosmetic products in advance to evaluate color payoff, texture, and durability before making a purchase. To meet this demand, cosmetic retailers offer a wide range of tester products. However, these testers are frequently used by an unspecified number of individuals, leading to increased hygienic vulnerability and ongoing concerns about microbial contamination and infection risks. Although the COVID-19 pandemic temporarily reduced the use of testers, cosmetic stores continue to offer tester products by implementing improved hygiene measures such as single-use testers, non-contact testing devices, and disinfectable dispensers [20].

According to previous reports, various pathogenic microorganisms have been detected in tester cosmetics, and some consumers have experienced skin irritation or infectious diseases after use [4,5]. In our survey, the majority of respondents reported having used lip cosmetic testers, while simultaneously acknowledging the potential for microbial contamination. The main reason for heightened concerns over microbial contamination was that testers are commonly applied to the back of the hand or directly to the lips to evaluate color, pigmentation, texture, and usability. Participants also perceived that the repeated use of testers by multiple individuals could introduce saliva and skin contact, increasing the risk of microbial contamination. In addition, most individuals with prior experience using lip cosmetic testers expressed greater concern about microbial infection susceptibility than product safety sensitivity. In particular, younger participants and those with higher levels of education exhibited greater microbial infection susceptibility. These findings indicate that health concerns related to the use of shared cosmetic products, such as testers, are considerable.

To analyze major pathogenic bacteria associated with oral and respiratory infections, we examined 30 opened lip cosmetic testers and 30 unopened products. Bacterial culture results revealed that none of the unopened products showed bacterial growth, while 18 out of 30 (60%) opened testers yielded bacterial colonies. According to Article 8 of the Korean Cosmetics Act [21], preservatives, colorants, and UV filters-ingredients that require special usage restrictions, must comply with specific usage standards. Cosmetic products often contain moisture and nutrients, making them susceptible to microbial and fungal growth. Preservatives are thus added to inhibit microbial proliferation, ensuring product stability and consumer safety. Commonly used antimicrobial agents include parabens, phenoxyethanol, sodium benzoate, sorbic acid, and chlorphenesin. The absence of bacterial growth in some of the opened tester products may be attributed to the presence of such preservatives. Nevertheless, among the eight target bacteria tested in this study, several were detected at relatively high frequencies despite the presence of antimicrobial agents.

Notably, the bacteria detected in the opened lip cosmetic tester products were species associated with oral and respiratory tract infections. In addition to bacteria, viruses and fungi (including yeasts and molds) are also common pathogens capable of causing human infections. However, due to differing culture requirements, this study focused solely on bacteria. Viruses are obligate intracellular organisms that rely on host cells for replication. As such, virus particles on the surface of products exposed to the environment are likely present in extremely low quantities, potentially falling below the limit of detection for PCR analysis. This may result in reduced sensitivity or failure of viral detection. Candida spp. have been detected in lip cosmetics due to cross-contamination via lip and hand contact [22]. Molds such as Aspergillus spp. and Penicillium spp. have been reported to contaminate solid or powder-based cosmetic products depending on storage conditions [23]. Because fungi have cell walls composed of chitin, additional pretreatment steps are required during nucleic acid extraction. Moreover, the oil and alcohol content in cosmetic products may interfere with nucleic acid extraction and PCR enzyme activity, which could further hinder the detection of viruses and fungi. A limitation of this study is that viral and fungal detection was not attempted due to differences in culture conditions and methodological constraints in analyzing contaminating microorganisms. However, we focused specifically on detecting eight bacterial species that could potentially be associated with the use of lip cosmetic testers. S. epidermidis and P. aeruginosa were the most frequently detected species, followed by S. aureus and S. mutans. The high detection frequency of S. epidermidis, a common skin commensal, appears to be attributable to contact-related transmission, whereas the frequent detection of P. aeruginosa, an environmental bacterium commonly found in moist habitats, is presumed to result from transient contamination due to frequent contact. S. pneumoniae was found in 22.2% of the samples, which may be attributed to the fact that the testers were collected during the winter and seasonal transition periods when respiratory infections are more prevalent. S. epidermidis is a common skin and mucosal commensal bacterium that can be transmitted through hand or skin contact. It is an opportunistic pathogen capable of causing various inflammatory conditions [24]. S. oralis and S. salivarius, though typically part of the normal oral flora, can act as opportunistic pathogens and have been implicated in conditions such as endocarditis [25]. S. mutans, a major resident of the oral microbiota, is a primary causative agent of dental caries due to its ability to form plaque on tooth surfaces [26]. P. aeruginosa is also an opportunistic pathogen that produces various cytotoxins and may cause pneumonia and otitis externa, especially in immunocompromised individuals [27]. S. aureus, another skin and mucosal commensal, can cause skin infections such as impetigo, folliculitis, boils, pustules, and abscesses, and it is also implicated in oral and pulmonary infections [28]. S. pneumoniae is transmitted via droplets or direct contact [29]. The detection of E. coli, a commonly used indicator of hygiene management, may indicate potential lapses in handling or hygiene practices after product opening. Moreover, under conditions of impaired host defenses, P. aeruginosa, S. aureus, E. coli, and S. pneumoniae are recognized as important human pathogens that can contribute to disease development. According to the “Regulations on Cosmetic Safety Standards” by the Korean Ministry of Food and Drug Safety, pathogenic bacteria such as E. coli, P. aeruginosa, and S. aureus should not be present in cosmetic products [30]. The European Union (EU; Standard number - International Organization for Standardization (ISO) 17516:2014, Title - Cosmetics — Microbiology — Microbiological limits, Publisher – ISO, Geneva, Switzerland, 2014) [31] and the U.S. Food and Drug Administration (FDA) [32] have established microbiological quality criteria for cosmetics, with the common principle that specific pathogenic microorganisms must not be detected and that the total microbial load should remain within acceptable limits to ensure product safety. For general products, the limits are defined as a total aerobic microbial count (TAMC) of ≤1000 CFU/g or mL, a total yeast and mold count (TYMC) of ≤100 CFU/g or mL, and the absence of pathogenic microorganisms such as S. aureus, P. aeruginosa, C. albicans, and E. coli in 1 g or 1 mL of product [31,32].

5. Conclusions

Most individuals who had previously used lip cosmetic testers exhibited greater microbial infection susceptibility than product safety sensitivity, showing heightened concern about infection risks from contaminated products. Bacterial analysis of opened lip cosmetic testers revealed a high frequency of disease-causing bacteria, emphasizing the potential health risks associated with their shared use. Although this study was limited to the detection of eight oral- and respiratory-associated bacterial species, the findings provide evidence that lip cosmetic testers can serve as significant vehicles for the transmission of various pathogenic microorganisms. Expanded surveys and microbiological analyses are needed to determine whether these results are generalizable across different countries. In addition to lip cosmetic testers, further investigations should address hygiene management practices and both vendor and consumer awareness regarding products that come into direct contact with the mucosa or skin. The implementation of hygiene measures, such as providing single-use samples or introducing sterilization devices designed to ensure user safety, is urgently warranted. Above all, this study underscores the necessity of extending existing microbiological standards and hygiene guidelines to encompass cosmetic tester products. The results of this study provide important evidence for the necessity of establishing public guidelines for the management of shared cosmetic testers and for promoting more hygienic practices among consumers when using cosmetic testers.