Some products use Erythrulose combined with the
DHA. Erythrulose works identically to
DHA on the skin surface, but develops more slowly. The two chemicals used together may produce a longer lasting sunless tan.
Dihydroxyacetone or Erythrulose may cause contact dermatitis. First time users of sunless tanning products should apply them to a small patch of skin and wait 24 hours before a full body application.
ref:http://en.wikipedia.