The only sunless tanner that has been approved by the FDA is dihydroxyacetone (DHA) – a clear 3-carbon sugar that triggers a chemical reaction on the surface of the skin. It affects the outermost layer, but does not damage skin below it. Marketing claims of light, medium, or dark tanning usually correspond with the level of concentration of DHA within the product (likely ranging from 3% to 10%). Sunless tanners are difficult to apply evenly, so a lighter shade may be a better choice for the do-it-yourself application. A tan usually develops within an hour of application but could take longer to fully develop. A DHA tan will last until the dead skin cells slough off, usually 5-7 days. In order to promote their products, some companies include extra ingredients such as moisturizers and sunscreens. Some include exfoliators to slough off the excess dead skin so that the product adheres to newer cells and may make the color last longer.