What reaction does DHA undergo to create a tan?

DHA, or dihydroxyacetone, is a common ingredient in sunless tanning products. When applied to the skin, DHA undergoes a chemical reaction primarily with the amino acids present in the outer layer of the skin. This reaction produces melanoidins, which are responsible for the brown pigmentation that mimics a natural tan.

The process of DHA reacting with amino acids in the skin is known as the Maillard reaction, and it leads to a tan that develops over a few hours after application. Understanding this reaction is crucial for tanning consultants, as they can better inform their clients about the science behind the tanning process and set realistic expectations for results.

Other reactions described in the options are not responsible for the tanning effect provided by DHA. While water is present in the skin, DHA's primary function is not to react with it. UV light does contribute to natural tanning but is not related to the efficacy of DHA. Lastly, while keratin is a component of the skin, it is the amino acids that directly engage with DHA to produce the desired tanning effect. This knowledge helps in ensuring optimal product use and customer satisfaction in the tanning process.