Chapter 25 Self tanning

Dihydroxyacetone (DHA), binding the amino terminal of epidermal proteins, imparts an orange-brown colour to the skin 3-10 h from the application. The degree of skin darkening is related to the DHA concentration, usually from 2.5 to 6.5%. The action mechanism of DHA involves the formation of so-called melanoids, chromophores generated in the upper layers of the stratum corneum. Besides the browning effect, useful for cosmetic purposes or for masking hypopigmented macules of vitiligo, DHA application protects the skin against long-wave ultraviolet (λ>320 nm) showing an UVA protection factor from 1.7 to 2.2, depending on its concentration. The DHA does not protect against UVB (λ<320 nm). DHA containing sunscreens are useful to prevent polymorphous light eruptions or erythropoietic protoporphyria and to give a tanned look to hair-skinned individuals avoiding harmful sun exposures.