Persistent Pigment Darkening

The persistent pigment darkening (PPD) response is a longer lasting response of individuals with pigmented skin after irradiation with UVA radiation. The response is evaluated 2-24 h after UVA exposure. The PPD protection factor, proposed by Chardon et al. 23 , is the ratio of the UVA dose required to produce the PPD response, with and without a sunscreen on the skin. The PPD test produces rapid results with moderately low doses of UVA. The response is stable and reproducible as in the case of...