TANNING IN HUMAN SKIN TYPES II AND III OFFERS MODEST PHOTOPROTECTION AGAINST ERYTHEMA

We have investigated the photoprotective properties of tanning using e rythema as an endpoint, Previously unexposed buttock skin sites of 16 young, healthy adults (8 skin type II, and 8 skin type LII) were expos ed daily (Mon-Fri) for 2 weeks to 0.5 and 0.75 minimal erythema doses (MED) of solar-simulated radiation (SSR), Erythema and melanin levels were assessed daily both visually and quantitatively using a reflectan ce device. One week after the last tanning treatment, MED reassessment s were made on pretreated sites and on adjacent nontreated sites, incl uding sites from which stratum corneum was removed by tape stripping. Compared to skin type II, similar daily SSR treatments produced less e rythema and more evident tanning in skin types III. Independent of ski n type, all volunteers showed an increased MED value when assessed on the 0.75 MED- and 0.5 MED-treated sites compared to the MED value asse ssed on adjacent untreated sites. We express any increase in MED as an induced protection factor (IPF), i.e. (MED post-tan/MED pre-tan). Our data show mean IPF of 1.4 and of 2.1 in the 0.5 and 0.75 MED-treated sites respectively, in skin types II. Similar values were obtained in skin types III with IPF of 1.5 and 2.3 for the 0.5 and 0.75 MED-treate d sites, respectively. In all cases, removal of the stratum corneum lo wered the IPF by about 20%, Our results show that SSR-induced melanoge nesis, whether in skin type II or III, offers only moderate protection against erythema and suggest that SSR-induced stratum corneum thicken ing affords less photoprotection than tanning.