Every now and then I get a question about what makes a tanner tick, so I thought I'd take a minute to explain the process, and clear up a few misconceptions as well.

What Makes It Work

Regardless of what claims a self-tanner makes about unique formulations, all tanners use the same active ingredient: dihydroxyacetone (DHA). DHA is a colorless sugar that's often derived from sugar beets or sugar cane. When applied to the skin, it reacts with the amino acids in the skin's very top layer (i.e., the dead skin surface layer), turning it brown.

DHA's effects on skin were first discovered, albeit accidentally, by German scientists in the 1920s. The first sunless tanning product was introduced by Coppertone in the 1960s, and turned skin an unfortunate shade of beta-carotene-overdose orange. Since then, cosmetic scientists have gotten quite a bit better at refining DHA, resulting in a more natural looking outcome.

DHA concentrations range from about 1-15%. Gradual self tanners contain low percentages of the ingredient, allowing you to build your tan over several days; full-strength formulas like St. Tropez have more, and give you a darker tan in one application.

Why It Smells

That telltale self-tanner aroma will make its presence known a couple of hours after application (sometimes sooner). It's just what happens when the DHA starts reacting with your skin, so not much can be done about it.

But it isn't the DHA alone that makes some tanners so nauseating. When heavy fragrances are added to the product, well, it's a toss-up. Some scents manage to mask the DHA smell fairly well (Victoria's Secret Bare Bronze) or work with it (L'Oreal Sublime Glow). But many times, the added fragrance just makes the overall effect worse (Lancome's mousse formula, the original scent of Jergens Natural Glow...blech).

A good bet is to find one that's completely unscented - my pick is Famous Dave's. It'll smell of DHA after a few hours, but since there's no other fragrance for it to interact with, it's far more tolerable.

How Long It Lasts

Since DHA only reacts with the very top layer of your skin, your faux tan will only last for a few days, until your skin naturally exfoliates itself (or you scrub it off). If your tan happens to last longer, it's not due to some superior formulation - it's just because your body hung on to that layer of skin a little longer.

You can prolong the life of your tan with a touch-up layer of gradual tanner every couple of days, at least until you're ready to scrub and start over. For more tips, check out The Art of the Tan: Prep, Application, and Maintenance.

And, check out the Beauty Addict Self Tan archives for loads of self-tanner reviews.

Any other questions about self-tanners? Ask in the comments!