Spray-On Tanning, Considered

Credit...Victoria Roberts

Q. How do self-tanning products change the color of my skin?
Are they safe?

A. The key ingredient of many effective self-tanning products is a chemical derived from sugar called dihydroxyacetone, or DHA.

It works by reacting with amino acids in the dead cells of the thin, outermost layer of the skin, called the stratum corneum, to produce pigments called melanoidins. The color lasts three to seven days, until those cells are sloughed off.

Using products with DHA to get a tan is safer than sun exposure. DHA is approved by the Food and Drug Administration and is considered safe by most dermatologists, but only when the products are used as approved.

They should be applied only to the surface of the skin, avoiding eyes, lips and mucous membranes. Spray-tanning booths are not recommended, even when nose plugs and goggles are used.

Some products with high concentrations of DHA increase susceptibility to cell damage from reactive forms of oxygen produced by sunlight, called free radicals, for 24 hours after application. For this reason, some researchers have recommended reducing exposure to the sun if you use self-tanners.

In any case, self-tanning products are not a substitute for sun blockers, because their sun protection factor, or S.P.F., is minimal and short-lived. “It is extremely important to apply sunscreen” after using self-tanners, according to a review of tanning methods in The Journal of Clinical and Aesthetic Dermatology. question@nytimes.com