Definition
DHA (dihydroxyacetone) is a colourless sugar that reacts with amino acids in the outermost layer of the skin to produce a temporary bronze colour. It is the active ingredient in nearly every modern self tan.
why it matters.
DHA is what makes self tan work, full stop. It has been approved for topical cosmetic use by the FDA since 1977 and has more than fifty years of dermatological research behind it. The depth of your tan comes from the percentage of DHA in the formula.
When you see "Ultra Dark" on a label, you’re seeing a higher concentration of DHA.