Factors influencing sunless tanning with dihydroxyacetone.
BACKGROUND
Sunless tanning preparations have been used for more than 50 years and are still very popular because they provide temporary pigmentation resembling an ultraviolet-induced tan. The pigment is the product of reactions between dihydroxyacetone (DHA) and amino acids in the stratum corneum.


OBJECTIVE
To understand the factors that influence the reactions of DHA with amino acids in the stratum corneum with the ultimate goal of producing pigmentation with greater photoprotection.


METHODS
The influence of hydration and/or oxygen on the development of DHA-induced pigment was assessed in vivo using an occlusive dressing and ex vitro on human epidermal preparations. Two spectroscopic techniques, diffuse reflectance and fluorescence emission, were used to monitor the extent of pigment development. The optimal relative humidity for DHA-induced pigmentation was assessed on the epidermal preparations. The formation of products from reactions between DHA and nine amino acids was studied in solutions buffered at pH 5 and 7.


RESULTS
Development of DHA-induced pigmentation was inhibited by a 24-h occlusive dressing but appeared after its removal, indicating that DHA was still present. High hydration but not the absence of oxygen inhibited coloration of occluded skin. The extent of pigmentation did not vary in a simple manner with hydration, as pigment formation was positively correlated with humidity from 0 to 75% but negatively correlated from 75 to 100%. Lysine, glycine and histidine reacted most rapidly with DHA, with reaction rates greater at pH 7 than at pH 5. The products absorbed with maxima at wavelengths up to 340 nm.


CONCLUSIONS
These results indicate that extent of hydration, pH and availability of certain amino acids influence the development of DHA-induced pigmentation in the stratum corneum and suggest that manipulation of these factors might produce pigmentation with greater photoprotection.
Nguyen
B-C
BC
Wellman Laboratories of Photomedicine, Department of Dermatology, Massachusetts General Hospital, WEL-224, Harvard Medical School, 50 Blossom Street, Boston, MA 02114, USA.
Kochevar
I E
IE
D000596:Amino Acids / Q000378:metabolism*; D003879:Dermatologic Agents / Q000378:metabolism / Q000494:pharmacology*; D004098:Dihydroxyacetone / Q000378:metabolism / Q000494:pharmacology*; D004817:Epidermis / Q000378:metabolism; D006801:Humans; D006813:Humidity; D006863:Hydrogen-Ion Concentration; D010100:Oxygen / Q000494:pharmacology; D012880:Skin Pigmentation / Q000187:drug effects*; D013050:Spectrometry, Fluorescence; D013473:Sunscreening Agents / Q000737:chemistry
D000596:Amino Acids; D003879:Dermatologic Agents; D013473:Sunscreening Agents; D004098:Dihydroxyacetone; D010100:Oxygen