Abstract
Recently it has been recognized that UVA protection would be one of the targets in the cosmetic industry because UVA causes pigmentation, photoaging or augmentative effects to responses by UVB. Furthermore, consumers have demanded to know what degree of protective efficacy against UVA each sunscreen had. Thus, we, Japan Cosmetic Industry Association-Ultraviolet Task Force, attempted to establish the standard test methods in Japan.
The skin responses in Japanese were investigated after exposure to UVA. Immediate pigment darkening was elicited immediately after exposure to a small amount of UVA, and they were faded out rapidly. However, black tanning on the site exposed to large amount of UVA turned to brown about 2 hrs after exposure and this tanning was stable. On the other hand erythema didn't appear in almost all volunteers. From these results we selected the tanning observed between 2 and 4 hrs after exposure as a marker in the UVA test method. This tanning was termed “persistent pigment darkening, ” and “minimal persistent pigment darkening dose” (MPPD) is the minimal amount of UVA required to elicit persistent pigment darkening. The protection factor of UVA (PFA) was expressed as a ratio of MPPD on a protected site to that on a non-protected site.
Next, we selected standard sample and then investigated the effects of observation time after exposure, skin type of volunteers and light sources of UVA on PFA using the standard sample (including 3% p-methoxycinnamic acid 2-ethylhexyl and 5% 4-tert-butyl-4′-methoxybenzoylmethane). The results showed that PFA didn't depend on these factors. The obtained PEA of the standard sample was 3.75 (SD: 1.01).
Based on these results, we established the standard test methods for UVA protection. Since these PFA values do not directly reflect the preventive effect on sunlight induced tanning in actual daily life, we decided that the grade of UVA protective potency of sunscreens should be labeled as PA+, PA++, PA+++ depending on their potential.
