Tanning is a popular pass time, but it is well known to be unsafe. There is no doubt that tanning in the sun contributes to skin cancer and ugly wrinkled skin. Are there safe alternatives? Yes, self-tanning or sunless tanning creams are an interesting option.
Self-tanning creams all contain a chemical known as dihydroxyacetone (DHA). This chemical was originally discovered in the 1920’s as a possible substitute for sugar in diabetics by Procter & Gamble. Dr. Eva Wittgenstein noted that when the sweet material splashed on the skin with chewing, the skin turned brown and the brown color could not be removed with washing and rubbing. Also, the saliva turned the skin brown! This side effect made the substance unsuitable as a sugar substitute. The chemical was not marketed until the 1950’s when the first self-tanning cream was introduced into the marketplace. The first self-tanning creams were met with little enthusiasm, however, since the color was an unsightly orange.
The reaction that occurs allowing the skin to turn is rather complex. The skin turns brown because it causes melanoidins to form that are similar to the brown pigment in the skin, such as melanin. The browning reaction that occurs when the sugar is put on the skin is known as the Maillard reaction, named after Louis-Camille Maillard who first described the reaction in 1912. The Maillard reaction is currently defined as the reaction of skin proteins with sugars to form the artificial tanned appearance.
Self tanning products can be purchased as creams, lotions, and sprays. They can be made to provide a light brown color, medium brown color, or dark brown color. The shade can be varied by changing the concentration of the sugar, known as DHA. Lower concentrations of DHA produce a light brown color while higher concentrations produce darker shades.
As might be expected, skin areas with more protein stain a darker color. For example, crusty skin growths will also darken with the self-tanning cream making the brown appear uneven. Protein rich areas of the skin, such as the elbows, knees, palms, and soles, also stain more deeply. For this reason, it is advisable to remove all dead skin through exfoliation prior to self-tanning cream application. This can be accomplished with a skin scrub containing polyethylene beads, a textured cloth, or a hydroxy acid moisturizer. Take note, however, as self-tanning creams will stain the hair and nails.
The brown color is usually visible within 1 hour after application, but maximal darkening may take 8-24 hours. Many self-tanning preparations contain a temporary dye to allow the user to note the sites of application and to promote even application.
There are several drawbacks to the currently marketed self-tanning products. One drawback is the limited control over the final color. This has been corrected by increasing the protein content of the outer skin. One formulation contains a solution to add protein to the skin just before applying the sugar. This protein interacts with the sugar deepening the color of the tan.
Another problem with self-tanning preparations is the difficulty in applying the cream or lotion evenly. This has been improved by applying the self-tanner as a spray. This service is offered in some tanning salons. The customer enters a self-contained shower where spray heads mist the DHA liquid over the entire body is an even film. Areas of the body where a tan is not desired, such as the palms, soles, between the toes, etc., are covered with petroleum jelly. These treatments cost approximately $40 and must be repeated every 2 weeks. The procedure is entirely safe, but self-tanners can only confer an SPF of 3, which is not adequate sun protection. If you use self-tanning products, you must continue to use a sunscreen.
Self-tanners also have a bad smell. It is difficult to mask the bad smell with fragrance ingredients, so this problem has not been overcome.
Many dermatologists are advocating the use of sunless tanning products as an alternative to sun exposure. While sunless tanning products are able to simulate a beautiful tan, there are some specifics that are important for the consumer to understand.
Sunless tanning products are all based on the same chemical known as dihydroxyacetone, abbreviate DHA. DHA was originally discovered in the 1920’s as a sugar substitute for glucose. It was rediscovered in 1957 when Eva Wittgenstein, MD, a physician at a children’s hospital discovered the tanning properties of DHA. Dr. Wittgenstein was studying the effect of orally administered DHA on a childhood glycogen storage disease when she noticed that the children were developing a brown color on the skin where they had spit up the sweet syrup. She subsequently applied the liquid to her own skin and noticed the “tanned” color. The product was commercialized in 1959 as a shaving lotion known as “Man-Tan.” It was a tremendous success, but the raw DHA was rather expensive at $2000 per kilogram.
DHA is the basis for all presently marketed sunless tanning products and is a 3-carbon sugar that is manufactured as a white, crystalline hygroscopic powder. DHA is formed when glycerol is fermented by Gluconobacter oxydans. It interacts with amino acids, peptides, and proteins to form chromphobes known as melanoidins. Melanoidins structurally have some similarities to skin melanin, but are not photoprotective. DHA only interacts only with the stratum corneum as the entire brown color can be removed by tape stripping the skin. Thus, the thicker the stratum corneum, the more deeply the skin will pigment. For this reason, the brown is less intense on the face where the stratum corneum is thin and more intense on the elbows where the stratum corneum is thicker.
The pH level of the skin and the formulation can also change the color of the DHA-induced skin stain. If the skin or the formulation is alkaline, the DHA color will be more orange. Conversely, if the skin or the formulation is acidic, the DHA color will be more natural in appearance. The optimal pH for the best color development is 5-6.
The amount of water in the formulation can also affect the DHA color. If too much water is present, the DHA color will be lighter. For this reason, DHA products are not formulated with glycerin that inhibits the browning reaction. It has been noted that propylene glycol and sorbitol increase the tanning intensity.
The browning reaction that occurs when DHA is exposed to keratin protein is known as the Maillard reaction. DHA is technically categorized as a colorant or colorless dye. It reacts with amines, peptides, and free amino acids in the stratum corneum. The first step is the conversion of DHA to pyruvaldehyde with the elimination of water. Then the keto or aldehyde interacts with skin keratin to form an imine. The remaining specifics of the reaction are still unknown, but the resulting products are cyclic or and linear polymers that have a yellow or brown color.
The chemical reaction is usually visible within 1 hour after DHA application, but maximal darkening may take 8-24 hours. Many self-tanning preparations contain a temporary dye to allow the user to note the sites of application and to promote even application, but this immediate color should not be confused with the Maillard reaction.
As mentioned previously, the brown color produced by self tanners does not provide the same photoprotection as melanin. However, the DHA polymers absorb long wavelength UVA in the 300-380nm range. DHA used to be listed on the sunscreen monograph, but it has since been removed since DHA can only product an SPF of 3-4. It is important to remind patients that they will still sunburn and tan while using a self tanner and must still use a sunscreen over exposed skin.
DHA can be combined with organic sunscreens that do not contain amino groups, such as octyl methoxycinnamate, homosalate, octocrylene, and benzophenone. It also can be combined with inorganic sunscreens, such as zinc oxide and titanium dioxide. The challenge with inorganic sunscreen combinations is that the zinc oxide and titanium dioxide can discolor brown in the bottle if 5% DHA is combined with 5% inorganic sunscreen after only a few days.
DHA is usually added to a creamy base in concentrations of 3-5%. Lower concentrations of DHA produce mild tanning while higher concentrations produce greater darkening. This allows self-tanning creams to be formulated in light, medium, and dark shades. The depth of color produced by self-tanning creams can be enhanced by increasing the protein content of the stratum corneum. This is accomplished by applying a sulfur-containing amino acid, such as methionine sulfoxide, to the skin just before applying the DHA.
DHA is a nontoxic ingredient both for ingestion and topical application. It has a proven safety record with only a few reported cases of allergic contact dermatitis. In the 1920’s, it was determined that large quantities of oral DHA did not produce toxicity and the LD50 in rats is over 16 grams per kilogram. It is interesting to note that the phosphate of DHA is one of the intermediates in the Kreb’s cycle known as dihydroxyacetone monophosphate. Topically applied DHA reacts immediately upon contact with the stratum corneum amines and is not absorbed for this reason. DHA has not been detected in the urine or serum of volunteers following topical application.
The staining reaction that occurs with DHA is limited strictly to the stratum corneum and can be readily removed with tape stripping and exfoliation. Thus, the product must be reapplied daily to maintain the optimal skin darkening. There are no known side effects, except for possible irritation, from frequent application. The DHA does have a distinct odor, which is difficult to mask with fragrances.
The American Academy of Dermatology has begun to advise the use of self tanners in some of its safe sun messaging. As consumers hear these public service announcements, more questions regarding the skin use of DHA may arise. It is hoped that this article has provided some of the more important details regarding DHA and its formulation into self tanning preparations. The formulations can be used safely, but do not provide adequate photoprotection unless combined with a sunscreen. A natural appearing tan can be created by artistically applying the self-tanning cream evenly. Care should be taken to apply less product to easily stained areas, such as the ankles, knees, elbows, and toes. The hands should be washed immediately following application to prevent unnatural staining of this skin surface. The product should not be applied to the hair or nails. These few simple instructions can simulate a tanned appearance without the photoexposure.