A fake tan is affected by a few factors, including skin thickness at the outermost layer (the stratum corneum or horny layer), the skin's pH levels, and how highly concentrated amino acids are in one's skin. When the stratum is very thick, as at the elbows, the tan is intense; when the horny layer is thin, such as the face, the tan is less intense. An alkaline pH turns the tan orange, whereas a slightly acidic pH reduces color problems. Since DHA reacts with the skin's amino acids, varying levels among individuals will affect the color result. [Manufacturers generally suggest that you apply a DHA product to freshly exfoliated skin]