Dihydroxyacetone

Dihydroxyacetone (DHA), also known as glycerone, is a simple saccharide (a triose) with formula .
DHA is primarily used as an ingredient in sunless tanning products. It is often derived from plant sources such as sugar beets and sugar cane, and by the fermentation of glycerin.
Chemistry
DHA is a hygroscopic white crystalline powder. It has a sweet cooling taste and a characteristic odor. It is the simplest of all ketoses and has no chiral center. The normal form is a dimer (2,5-bis(hydroxymethyl)-1,4-dioxane-2,5-diol). The dimer slowly dissolves in water, whereupon it converts to the monomer. These solutions are stable at pH's between 4 and 6. In more basic solution, it degrades to brown product.
This skin browning effect is attributed to a Maillard reaction. DHA condenses with the amino acid residues in the protein keratin, the major component of the skin surface. When injected, no pigmentation occurs, consistent with a role for oxygen in color development. The resulting pigments, which can be removed by abrasion, 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.
Preparation
DHA may be prepared, along with glyceraldehyde, by the mild oxidation of glycerol, for example with hydrogen peroxide and a ferrous salt as catalyst. It can also be prepared in high yield and selectivity at room temperature from glycerol using cationic palladium-based catalysts with oxygen, air or benzoquinone acting as co-oxidants. Glyceraldehyde is a structural isomer of dihydroxyacetone.
Biochemistry
Its phosphorylated form, dihydroxyacetone phosphate (DHAP), takes part in glycolysis, and it is an intermediate product of fructose metabolism.
History
DHA was first recognized as a skin coloring agent by German scientists in the 1920s. Through its use in the X-ray process, it was noted as causing the skin surface to turn brown when spilled.
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. Wittgenstein continued to experiment with DHA, painting liquid solutions of it onto her own skin. She was able to consistently reproduce the pigmentation effect, and noted that DHA did not appear to penetrate beyond the stratum corneum, or dead skin surface layer (the FDA eventually concluded this is not entirely true). Research then continued on DHA's skin coloring effect in relation to treatment for patients with vitiligo.
Winemaking
Both acetic acid bacteria Acetobacter aceti and Gluconobacter oxydans use glycerol as a carbon source to form dihydroxyacetone. DHA is formed by ketogenesis of glycerol. It can affect the sensory quality of the wine with sweet/etherish properties. DHA can also react with proline to produce a "crust-like" aroma. Dihydroxyacetone can affect the anti-microbial activity in wine, as it has the ability to bind SO2.
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 suit 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 still associate sunless tanning with fake-looking orange tans.
In the 1970s the United States 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 created 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, DHA is the main active ingredient in many sunless tanning skincare preparations. Lotion manufacturers also produce a wide variety of sunless tanning preparations that replace DHA with natural bronzing agents such as black walnut shell. DHA 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 20%. Most drugstore products range from 3% to 5%, with professional products ranging from 5% to 20%. 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. 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.
References
External links
How Stuff Works
US FDA/CFSAN - Tanning Pills
American Academy of Dermatology on Self Tanners
DHA and Vitiligo
New Zealand Dermatological Society recommends sunless tanners
Cosmetics chemicals
Diols
Alpha-hydroxy ketones
Trioses