UVA protection efficacy of sunscreens can be determined by thepersistent pigment darkening (PPD) method

Abstract

The results show PPD to be a stable end point inducible by all the UVA wavelengths, not affected by fluence rate, i.e. a reliable endogenous UVA dosimeter in the skin.

Analysis of Ultraviolet Radiation Wavelengths Causing Hardening and Reduced Elasticity of Collagen Gels In Vitro

“…Currently, two standard test methods for efficacy of UVA protection are used internationally: the observation of persistent pigment darkening (PPD), which presents as immediate pigment darkening (IPD) 2-24 h after exposure in humans with skin type II to IV (in vivo) [5][6][7][8]; and the creation of an absorption curve of thin film or Transpore™ tape that has had the test material applied constant negative pressure, and the immediate retraction (Ur) of the skin when the pressure is released. The smaller the ratio of the immediate retraction to the maximal extension (Ur/Uf) of the sample, the lower is the biological elasticity.…”

Photoprotection

“…128 The more commonly used in vivo methods are IPD, 129 PPD, 130,131 and protection factor in UVA. 132 Assessment of erythema induced after topical psolaren application and UVA exposure is no longer used because of concern for carcinogenicity.…”

About Suncare Products

“…If the reading takes place at a maximum of 2 hours after irradiation, we refer to the IPD (immediate pigment darkening) method. If the reading is taken later, we can refer to it as the PPD (persistant pigment darkening) method [54,55,56]. …”