At the elbows and knees, the skin is particularly dense, so there are more amino acids that can react with the natural self-tanning agents. When applying the self-tanner to these areas, be careful not to use excessive amounts of product. Tip: If too much products is dispersed, use a tissue to blot off any excess. Also, leave out hairline, eyebrows, as well as fingernails and toenails, as they also react more strongly due to amino acids.