The most effective spray tanning products contain dihydroxyacetone, or DHA, a carbohydrate derived from glycerin or other plant sources such as sugar cane. Although it’s colorless, DHA has a way of interacting with the amino acids naturally found in your skin cells to make your skin become darker. The more DHA that you apply to your skin when you spray tan, the darker your skin becomes. Approved by the FDA, DHA is a common ingredient in spray tan formulas and is safe for external use on your skin.