The skin is made up of two main layers: the epidermis on the outside and the dermis on the inside. The epidermis is further broken down into two layers: the innermost “stratum basale” and the outermost “stratum corneum”. Dihydroxyacetone (DHA), the active tanning ingredient found in all spray on tan solutions and self-tanning products, is a colourless sugar that interacts with the dead skin cells in the stratum corneum of the epidermis to produce a colour change. This colour change generally lasts for approximately 7 -10 days from the initial application.