Revised: January 19, 2013
Accepted: January 23, 2013
Published online: February 2, 2013
AIM: To describe the frequency and biophysical response of sensitive skin in Mexican subjects, using the lactic acid test.
METHODS: The lactic acid stinging test was applied to 250 healthy volunteers, both sexes, 18 years of age or older, without any active dermatoses on the test site. Volunteers were university students, workers of public institutions, and general population from San Luis Potosi, Mexico. Participants were not excluded based on socioeconomic status. Demographic data were obtained through a questionnaire. Skin phototype was obtained through colorimetry. Subjects were randomized to receive 10% lactic acid on one nasolabial fold and placebo on the other side. The presence and intensity of adverse sensations, such as itching, burning, or stinging, was evaluated through a 10-point Visual Analogue Scale (VAS) prior to treatment and at 3, 5, 8 and 10 min after the intervention. Subjects with a VAS of 2 or higher were considered positive for the test. A VAS lower than 2 was considered a normal response to skin manipulation. Simultaneously, biophysical changes and barrier function were assessed by colorimetry, transepidermal water loss (TEWL), and capacitance. To decrease measurement variations by skin manipulation, the nasolabial fold was segmented in four areas of 1 cm2 for each time measurement. Descriptive analyses were made using central tendency measures. Analyses of data were performed using two-tailed χ2 test, Fisher’s test, t-test, logistic regression, or Mann-Whitney U test for non-parametric values between groups.
RESULTS: Of the included 246 subjects, 68% were women and the mean age was 32 years. The most frequent skin phototype was V (ranges II-V). Thirty-six percent of the subjects identified themselves as having sensitive skin. Fifty-two percent of the subjects were positive to the lactic acid stinging test, with a mean VAS of 4.5 at 3 min. Subjects with the self-diagnosis of sensitive skin were more likely to be positive for the test (80% vs 36%, P < 0.001). Lighter skin phototypes (types II and III) showed a higher response to the test compared to darker skin tones (type V; OR = 0.88, P < 0.001). There were no statistical differences in baseline biophysical measurements. At 3 min, TEWL was significantly higher in subjects positive to the test (27.5 vs 23.7, P < 0.05). At 5 min, TEWL and capacitance showed statistical differences (26.0 vs 22.4, P < 0.05, and 239 vs 179, P < 0.05, respectively). After 5 min, values tended to return to baseline levels in both groups.
CONCLUSION: Sensitive skin is frequent in our population. Darker skin phototypes have a lower prevalence of this syndrome, probably due to inherent differences in skin barrier function.
Core tip: Self-diagnosed sensitive skin can be found in one-third of Mexican subjects, but using the lactic acid stinging test, we identified a prevalence of 50%. Baseline biophysical measures did not predict the test response, but alterations in subsequent measurements support the hypothesis of a dysfunctional skin barrier. One subgroup presented a slow response to the test, suggesting that other pathways, such as an altered neurosensitive response, are involved. This study indicates a higher prevalence of sensitive skin in subjects with lighter skin phototypes compared to darker ones. These findings suggest that pigmentation may confer a protective mechanism against sensitive skin.