Dihydroxyacetone
Dihydroxyacetone (also known as DHA) is a simple carbohydrate that is primarily used as an ingredient in sunless tanning products.  It is often derived from plant sources such as sugar beets and sugar cane, by the fermentation of glycerin.

# Chemistry
DHA is a triose carbohydrate chemical formula C3H6O3. It is a hygroscopic white crystalline powder.  It has a sweet cooling taste and a characteristic odor.  It is the simplest of all ketoses and, having no chiral center, is the only one that has no optical activity.  The normal form is a dimer which is slowly soluble in one part water and 15 parts ethanol.  When freshly prepared, it reverts rapidly to the monomer in solution.  The monomer is very soluble in water, ethanol, diethyl ether and acetone.
DHA may be prepared, along with glyceraldehyde, by the mild oxidation of glycerol, for example with hydrogen peroxide and a ferrous salt as catalyst.

# Biological role
Its phosphate form, dihydroxyacetone phosphate (DHAP) takes part in glycolysis.
When combined with pyruvate,  DHA is sold as an athletic nutritional supplement which is claimed to be an orally administered fat-burner, which also increases lean muscle mass.

# Uses
DHA was first recognized as a skin coloring agent in the 1920s, by German scientists. Through its use in the X-ray process, it was noted as causing the skin surface to turn brown when spilled. World War II began, and further research in this area temporarily halted as scientists contributed their resources to the war effort.
In the 1950s Eva Wittgenstein at the University of Cincinnati did further research with dihydroxyacetone.  Her studies involved using DHA as an oral drug for assisting children with glycogen storage disease. The children received large doses of DHA by mouth, and sometimes spat or spilled the substance onto their skin. Healthcare workers noticed that the skin turned brown after a few hours of DHA exposure.
Eva Wittgenstein continued to experiment with this unique substance, painting DHA liquid solutions onto her own skin. She was able to consistently reproduce the pigmentation effect, and noted that DHA did not penetrate beyond the stratum corneum, or dead skin surface layer.
Additional research studied DHA's skin coloring effect in relation to treatment for patients suffering from vitiligo.
This skin browning effect is non-toxic, and similar to the Maillard reaction. It is more commonly seen in the food preparation industry, and was described in 1912 by Louis-Camille Maillard.
DHA reacts chemically with the amino acid groups, which are part of the protein containing keratin layer on the skin surface. Various amino acids react differently to DHA, producing different tones of coloration from yellow to brown. The resulting pigments are called melanoidins. These are similar in coloration to melanin, the natural substance in the deeper skin layers which brown or "tan", from exposure to UV rays.

## Winemaking
Both acetic acid bacteria A. aceti and G. oxydans use glycerol as a carbon source to form dihydroxyacetone.
DHA is formed by ketogenesis of glycerol into dihydroxyacetone (Eschenbruch & Dittrich, 1968; Drysdale & Fleet, 1988).  It can affect the sensory quality of the wine with sweet/etherish property. DHA can also react with proline to produce a "crust-like" aroma (Margalith, 1981; Drysdale & Fleet, 1988; Boulton et al., 1996). Dihydroxyacetone can affect the anti-microbial activity in wine, as it has the ability to bind SO2 (Eschenbruch & Dittrich, 1968).

## Sunless tanning
Coppertone introduced the first consumer sunless tanning lotion into the marketplace in the 1960s. This product was called Quick Tan or QT. It was sold as an overnight tanning agent, and other companies followed with similar products. Consumers soon tired of this product due to unattractive results such as orange palms, streaking and poor coloration. Because of the QT experience, many people today still associate sunless tanning with fake-looking orange tans.
In the 1970s the Food and Drug Administration (FDA) added DHA permanently to their list of approved cosmetic ingredients.
By the 1980s new sunless tanning formulations appeared on the market, and refinements in the DHA manufacturing process creating products that produced a more natural looking color and better fading.
Consumer concerns surrounding damage associated with UV tanning options spurred further popularity of sunless tanning products as an alternative to UV tanning. Dozens of brands appeared on drugstore shelves, in numerous formulations.
Today, Dihydroxyacetone is the main active ingredient in all sunless tanning skincare preparations. It may be used alone or combined with other tanning components such as erythrulose. DHA is considered the most effective sun-free tanning additive.
Sunless tanning products contain DHA in concentrations ranging from 1% to 15%. Most drugstore products range from 3% to 5%, with professional products ranging from 5% to 15%. The percentages correspond with the product coloration levels from light to dark. Lighter products are more beginner-friendly, but may require multiple coats to produce the desired color depth. Darker products produce a dark tan in one coat, but are also more prone to streaking, unevenness, or off-color tones. The artificial tan takes 2 to 4 hours to begin appearing on the skin surface, and will continue to darken for 24 to 72 hours, depending on formulation type.
Once the darkening effect has occurred, the tan will not sweat off or wash away with soap or water. It will fade gradually over 3 to 10 days, in conjunction with the skin's normal exfoliation process. Exfoliation, prolonged water submersion, or heavy sweating can lighten the tan, as these all contribute to rapid dead skin cell exfoliation. (The dead skin cells are the tinted portion of the sunless tan.)
Current sunless tanners are formulated into sprays, lotions, gels, mousses, and cosmetic wipes. Professional applied products include Spray Tanning Booths, Airbrush tan applications, and hand applied lotions, gels, mousses and wipes.
DHA does not damage the skin, and is considered a safe skin coloring agent and nutritional supplement.  Contact dermatitis is rarely reported. Most cases of sensitivity are due to other ingredients in the skin product preparation, such as preservatives, plant extracts, dyes or fragrances.
DHA has been approved for cosmetic use by the FDA, the Canadian Health Ministry, and most of the EU member nations.
DHA-based sunless tanning has been recommended by Skin Cancer Foundation, American Academy of Dermatology Association, Canadian Dermatology Association and the American Medical Association