D-Erythrulose (also known as erythrulose) is a tetrose carbohydrate with the chemical formula C4H8O4. It has one ketone group and so is part of the ketose family. It is used in some self-tanning cosmetics, generally combined with dihydroxyacetone (DHA).
Erythrulose is a natural based keto-sugar which reacts with the amino acids in the keratin protein on the outer or dead surface layer of the skin. (the stratum corneum layer of the epidermis) This non-toxic reaction produces a temporary browning effect similar to the Maillard reaction. This is not a stain or dye, but rather a chemical reaction that produces a color change on all treated skin. The reaction is similar to the browning effect seen when a cut apple slice is exposed to oxygen.
The brown color is comparable to the appearance of a UV based suntan. Because the skin continually exfoliates itself, losing thousands of dead surface skin cells each day, the tan hue is temporary. The tan appearance typically lasts from 2 to 10 days depending on application type, and skin condition.
Erythrulose is a clear to pale yellowish liquid, which naturally occurs in red raspberries. According to the manufacturing company Centerchem, inc.  Erythrulose is manufactured from the aerobic fermentation of the bacterium Gluconobacter followed by extensive multi-step purification.
Erythrulose and dihydroxyacetone (DHA) are very similar in composition, and both react much the same way on the skin surface. Erythrulose produces a lighter and slower developing tan, taking 24 to 48 hours to complete development. When used alone, it fades faster than a DHA based sunless tan. Some people feel the final tone of erythrulose is slightly redder, and less bronze, than the DHA based tan. It may be less drying to the skin surface, helping provide a smoother fading tint. When combined with DHA, the resulting sunless tan is said to last longer, fade better, and provide a more cosmetically pleasing color tone. In sunless tanning products, it is incorporated at 1% to 3% levels.
Not all users develop a tan coloration from erythrulose, some may find that their fading is more uneven and blotchy, when this ingredient is used. Because of the added cost associated with this ingredient, some manufacturers feel it is an inefficient additive to the sunless tanning product line.
Individuals, who are sensitive to DHA, may be able to use erythrulose as a skin safe self-tanning replacement. Erythrulose is more expensive, and difficult to obtain. Because DHA and erythrulose are very similar in composition, it is not unusual for someone to be reactive to both DHA and erythrulose.
Erythrulose reacts on the skin's surface and does not seem to penetrate beyond the dead surface skin layers. Side effects are limited to occasional contact dermatitis in sensitive individuals. In many suspected cases of sensitivity, the reaction is related to other ingredients in the self-tanning product such as preservatives, dyes, fragrances or plant based additives and extracts.
Though erythrulose appears safe for use by all indications, it is not currently approved by the Food and Drug Administration (FDA) as a self tanning agent.