The Science of Spray Tanning: Sugar-Based Bronzing

How does a spray tan work? It all comes down to a chemical called dihydroxyacetone—or DHA, as its friends call it.

DHA is a kind of sugar; like food sugars, it can even be derived from sugar cane or beets. When applied, it begins to interact with amino acids in the skin's outer layer and turn it darker. But it's not living tissue that it's after: DHA associates mostly with the dead skin cells that cover your body. As these cells naturally fall off over time—which they do so frequently that after about a month, you have an entirely new epidermis—the color fades gradually until it's back to its original state, usually after a week or so. That's why salons recommend exfoliating before getting a spray tan: if you remove the skin cells that will be first to fall off anyway, your tan will last longer.

If spray-tan formulas all start out colorless, how can tanning salons offer different darkness levels? They simply up the concentration of DHA for clients who want to go darker. Those new to spray tanning should be careful, however. A higher concentration of DHA could mean a more orange tint, so starting at a light concentration and working your way up—or spacing out multiple applications at the same concentration—is wise. To counteract any tangerine tendencies, some formulas add a second chemical known as erythrulose. Derived from the sugars found in raspberries, erythrulose produces a reddish tint that complements the orange tones in DHA to create a more natural-looking color.