Cosmetic and dermatologic photoprotective O/W-macroemulsions or O/W-microemulsions containing dihydroxyacetone

An oil-in-water (O/W) emulsion (especially a microemulsion) containing dihydroxyacetone also contains : (A) an emulsifier whose lipophilicity is dependant on either pH or temperature; and (B) optionally also an oil- or aqueous phase-soluble or -dispersible emulsifier which is preferably other than of type (A) and which preferably acts as a W/O emulsifier. An oil-in-water (O/W) emulsion (especially a microemulsion) containing dihydroxyacetone also contains : (A) an emulsifier whose lipophilicity is dependant on either (i) pH (increasing or decreasing with increase or decrease in pH or vice-versa) or (ii) temperature (the lipophilicity increasing with increasing temperature and the hydrophilicity increasing with decreasing temperature); and (B) optionally also an oil- or aqueous phase-soluble or -dispersible emulsifier which is preferably other than of type (A) and which preferably acts as a W/O emulsifier.