Dihydroxyacetone (DHA) is a simple carbohydrate compound that has become the foundation of the modern sunless tanning industry. This small molecule is classified chemically as a triose sugar. DHA is the primary active ingredient used in nearly all lotions, sprays, and mousses designed to temporarily darken the skin without exposure to ultraviolet (UV) radiation.
Chemical Identity and Natural Sources
DHA is the simplest form of a ketose sugar and is a derivative of glycerol, a common organic compound. The DHA used in cosmetic products is often sourced from natural, plant-based origins, such as sugar beets or sugarcane. It is produced through a biotechnology process involving the bacterial fermentation of glycerin, a byproduct of these plant sources.
The Tanning Mechanism on Skin
The coloration produced by DHA on the skin is the result of a specific chemical process known as the Maillard reaction. This is a non-enzymatic browning reaction. The reaction is initiated when DHA comes into contact with the free amino acids and peptides that are present in the stratum corneum, which is the outermost layer of dead skin cells.
DHA acts as the reducing sugar in this process, reacting with the amine groups of amino acids like lysine and arginine. This chemical interaction produces a class of nitrogenous, brown-colored polymers called melanoidins. The formation of melanoidins is chemically similar to the browning that occurs when bread is toasted or meat is seared at high heat.
The color development is not instant and typically progresses over several hours, with maximal darkening occurring between 8 to 24 hours after application. Since the reaction is confined entirely to the stratum corneum, the resulting tan is only temporary. The color fades naturally and evenly as the dead skin cells of the outermost layer are shed through the body’s natural cell renewal cycle, usually lasting about 7 to 10 days.
Safety Profile and Regulatory Oversight
The United States Food and Drug Administration (FDA) has approved DHA for external application as a color additive in sunless tanning products. This regulation applies specifically to topical forms like lotions, creams, and gels, where the compound is applied directly to the skin’s surface. Studies have shown that DHA does not penetrate beyond the stratum corneum, making systemic absorption into the bloodstream unlikely when used as directed.
However, the safety profile changes when DHA is applied via spray or misting methods, such as in spray tanning booths. The FDA recommends that users shield their eyes, lips, and all mucous membranes, and should refrain from ingesting or inhaling the spray mist. Inhalation remains the primary concern, as it can potentially expose internal tissues to the reactive chemical.
Minor side effects from topical application are infrequent but may include mild skin irritation or localized allergic reactions in sensitive individuals. It is important to remember that a DHA-induced tan does not offer any protection against sun damage, unlike a natural tan. Therefore, the use of a separate broad-spectrum sunscreen remains necessary to protect the skin from harmful UV radiation.
Non-Tanning Uses
While sunless tanning is the predominant modern application, DHA has a history of other uses, including a brief period of medical investigation. In the 1920s, DHA was first studied as a potential sugar substitute for diabetic patients due to its sweet taste. It was during this research that a physician noted the skin-browning side effect, which eventually led to its cosmetic use.
Biologically, DHA has a fundamental role in metabolism in the form of dihydroxyacetone phosphate (DHAP). DHAP is a molecule that is an intermediate compound in the crucial process of glycolysis, which is how the body breaks down sugar for energy. DHA has also been explored in the past as a topical treatment for the skin condition vitiligo, though this use is not widely practiced today.