Relationship between skin parameters (darkness or thickness) and photoreaction of Chinese Han skin

Skin pigmentation and the stratum corneum are the two primary natural factors that protect against UV damage. Although several classification systems exist to quantify the ability of the skin to protect itself from damaging UV radiation, few reports have assessed skin parameters and photoreaction in persons of Han Chinese descent.

To understand the relationship between skin darkness, skin thickness, and photoreaction in Chinese Han subjects.

Thirty-one subjects were exposed to UVA and UVB. Minimal persistent pigment darkening dose (MPPD) and minimal erythema dose (MED) were obtained. Before the UV irradiation, the test sites were measured by the Mexameter MX 16, Chromameter CR400, and Skin B-ultrasonic to determine skin color and thickness>. Using the ratio of J(MPPD)/J(MED), we classified the subjects into four energy skin phototypes (ESPTs) and the skin parameters for each of these groups were analyzed.

Skin color and skin thickness were significantly different among the ESPTs. There was also a significant positive correlation between skin group and the skin color and thickness parameters (b*, melanin index [MI], thickness). As the ESPTs increased from ESPT A to ESPT D, the mean dose to achieve MED increased, while the MPPD decreased.

As the ESPTs increased from type A to type D, there was a proclivity to tan rather than burn. Similarly, the skin became darker and thicker as the phototype increased from A to D.