DHA, which stands for Dihydroxyacetone, is a colorless sugar that interacts with the amino acids present in the skin's top layer to produce a temporary bronze color. It is the primary active ingredient used in spray tanning solutions and is responsible for the color change. DHA has been used in cosmetic products since the 1960s and is considered a safe ingredient for topical use.

The percentage of DHA used in spray tanning solutions can vary between 6-14%, depending on the desired color and depth of the tan. The higher the percentage of DHA, the darker the tan will be. Most professional spray tanning solutions contain around 8-10% DHA.

The application of DHA spray tan involves a spray gun or airbrush that releases a fine mist of the solution onto the skin. The DHA reacts with the amino acids on the skin's surface to produce a brownish color, similar to the malliard reaction that occurs when food is cooked at high temperatures. The process is quick and can take around 10-15 minutes to complete, with the tan developing over the next 4-8 hours.

The malliard reaction is a chemical reaction that occurs when amino acids and sugars are exposed to heat, producing brown compounds responsible for the browning of cooked food. The process is similar to the reaction that occurs when DHA reacts with the amino acids on the skin's surface, producing a temporary bronze color. However, it is important to note that the malliard reaction is a natural process that occurs during cooking, while the DHA reaction is a cosmetic process that occurs through the application of a topical solution.