DHA condenses with the amino acid residues in the protein keratin, the major component of the skin surface.

These are similar in coloration to melanin, the natural substance in the deeper skin layers which brown or "tan" from exposure to UV rays.

[5] Its phosphorylated form, dihydroxyacetone phosphate (DHAP), takes part in glycolysis, and it is an intermediate product of fructose metabolism.

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.

[5] Lotion manufacturers also produce a wide variety of sunless tanning preparations that replace DHA with natural bronzing agents such as black walnut shell.

Darker products produce a dark tan in one coat, but are also more prone to streaking, unevenness, or off-color tones.

[5] The United States Food and Drug Administration (FDA) has approved DHA for topical application on the skin, but not for contact with eyes, lips, and mucous membranes.

Fragrances are often added to the formulation to mask the smell, which may lead to allergic reactions or worsen asthma symptoms.

Some products contain parabens as chemical preservatives that can cause rosacea and allergic contact dermatitis and act as weak estrogens.

A FDA report concluded that 11 percent of the applied DHA may penetrate into the living cells of the epidermis and dermis.

A previous study linked DHA to DNA damage, cell-cycle block, and apoptosis in living cells.

Antioxidants may be added to the formulation to produce a more natural tan, and may potentially counteract free radical damage.

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[13]).

Consumers soon tired of this product due to unattractive results such as orange palms, streaking and poor coloration.

[citation needed] In the 1970s the United States Food and Drug Administration (FDA) added DHA permanently to their list of approved cosmetic ingredients.

[14] 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.

[citation needed] Both acetic acid bacteria Acetobacter aceti and Gluconobacter oxydans use glycerol as a carbon source to form dihydroxyacetone.