Skin Tone Parameters as Possible Factors in Humectant Moisturizing Effectiveness

Prior work demonstrated differences in basal skin hydration related to skin tone parameter differences that included the melanin index (M), the erythema index (E), and the individual topology angle (ITA). The impact of these parameters on moisturization-induced hydration remains unclear. This study aimed to investigate whether basal skin tone influences moisturizer-related skin hydration.

M, E, and ITA were measured bilaterally at multiple anterior forearm sites of 30 young adults. The percentage water content (PWC) was determined by measuring the skin's dielectric constant to depths of 0.5 mm (PWC5) and 2.5 mm. PWC measurements were done before and four hours after applying four different humectant moisturizers. Analyses were conducted using the whole group and subgroups divided according to values below and above the median values for M, E, and ITA.

The whole group PWC increased at both depths. At 0.5 mm, it increased from its baseline of 46.4±10.2 to 51.5±9.1 (p < 0.001), a 12.6±11.3% increase. At 2.5 mm, PWC increased from its baseline of 39.1±6.6 to 40.6±6.1 (p < 0.001), a 4.2±5.7% increase. Both subgroups increased at 0.5 mm. However, percentage increases in PWC tended to be greater for subgroups with lower M and E and higher ITA. Considering gender, only males showed a significant positive correlation between the change in PWC5 and ITA (r = 0.584, p = 0.028), whereas females exhibited a uniform, non-skin tone-dependent response.

The findings suggest that lighter skin tones (higher ITA) may be associated with greater moisturizer-induced skin hydration. However, the differential gender responses may also indicate that male-female differences are involved and warrant further study.