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What’s that Stuff

What’s sunless tanner, and how does it impart that faux glow?

1 simple molecule holds the key to keeping a tan year-round

by Tien M. Nguyen
January 16, 2018 | A version of this story appeared in Volume 96, Issue 4

Bottles of lotion and sprays in a collage.
Credit: Shutterstock/C&EN

When physician Eva Wittgenstein discovered a chemical that could bronze skin rapidly, cosmetics and sunless tanners were probably the last thing on her mind.

Dihydroxyacetone has dominated the sunless tanning industry since its browning abilities were accidentally discovered in spit-up.
Structure of dihydroxyacetone.
Dihydroxyacetone has dominated the sunless tanning industry since its browning abilities were accidentally discovered in spit-up.

It was the mid-1950s, and Wittgenstein was conducting research at Children’s Hospital at the University of Cincinnati. She was studying children who had a rare metabolic disease and examining the effects of treating them with dihydroxyacetone, a simple, plant-derived, sugarlike molecule shaped like the letter m.

Her small patients took big doses of the stuff—up to 1 g/1 kg of body weight—sometimes causing the kids to spit up on themselves, which, if not cleaned up right away, left strange brown spots on their skin. Their clothes, however, remained unstained.

Intrigued, Wittgenstein poured a solution of dihydroxyacetone onto her own skin and confirmed its color-changing effects. She found that unlike makeup, which lies inert on top of skin, dihydroxyacetone reacts with it.

The reaction, it turns out, is related to one of chemistry’s tastiest transformations, called the Maillard reaction, responsible for the browned appearance of fried bacon and roasted coffee. In the Maillard reaction, sugars and amino acids react when heated to form a multitude of molecules, including some with a brownish hue. Similarly, the reaction that turns skin tan at room temperature occurs when the semisugar dihydroxyacetone reacts with amino acids like arginine, lysine, and histidine found in the outer layer of skin to produce yellowish-brown pigments called melanoidins.

Word of dihydroxyacetone’s browning abilities spread quickly to the cosmetic industry. By 1960, according to one newspaper report, at least a dozen sunless tanning products based on the molecule—with names like Man-Tan, Magic Tan, Tansation, and Tanorama—had been introduced to bronze the public.

Related: Suntan Addiction Explained

The products’ appeal grew as people recognized that sunbathing caused skin damage, though their understanding was flawed. At the time, many people thought that “good” ultraviolet-A (UV-A) radiation gave healthy-looking tans, while “bad” ultraviolet-B (UV-B) radiation caused burns and, in extreme cases, cancer, says David C. Steinberg, a chemist and regulatory expert on the cosmetics industry.

But the idea of safe UV exposure was a myth. In 2015, the U.S. Centers for Disease Control & Prevention reported that more than 90% of melanomas, the most dangerous type of skin cancer, are caused by both types of UV radiation.

By 2017, sunless tanning products were projected to bring in just over $1 billion in revenue worldwide. A national phone survey in 2004 estimated that 11% of adolescents in the U.S. had used such products in the past year, though some reports suggest that figure could be closer to 35% for young men and women.

As a high school student in the early days of self-tanning, Steinberg recalls one classmate’s unforgettable experience with a sunless tanning product. “She was yellow!” he says. Today’s tanners still use the same main ingredient, dihydroxyacetone, but the hues have been much improved.

These chromatic advances come from changes in the formulation of dihydroxyacetone, which is unstable. Cosmetic companies have improved the products by using different solvents and additives, lowering the pH of the mixture for better stability, and obtaining purer sources of dihydroxyacetone. Darmstadt, Germany-based Merck KGaA has produced pure dihydroxyacetone—via an enzymatic process with glycerol as the starting material—for self-tanning products almost since the sunless tanning industry’s start.

Related: Ushering cosmetics to the right spots

In 2013, Merck KGaA launched a non-dihydroxyacetone-based self-tanning product called RonaCare Bronzyl that works by enhancing a person’s melanin production. Its active ingredient is a compound called dihydroxy methylchromonyl palmitate. Bronzyl is more expensive than existing sunless tanners, and the results it yields are subtler and appear after about five to 10 days versus the typical two to six hours. The new tanner may offer safety advantages because unlike dihydroxyacetone, it can be formulated with sunscreen.

Sunless tanning is a much safer alternative to UV-powered sunbathing or sunlamp tanning, but it isn’t without risks.

Take, for example, the dangerous sunless tanning pills called French Bronze Tablets circulated in the late 1980s, a supply of which was eventually seized and destroyed by U.S. marshals. Ads in muscle magazines claimed that the tablets, which contained concentrated amounts of the food additive and pigment canthaxanthin rather than dihydroxyacetone, could give people golden tans within three weeks. What the ads didn’t mention was that, along with coloring users’ skins, it could also accumulate in their eyes, depositing yellow, sight-interfering crystals inside the retina. The effect reversed on its own, although eye crystals were detected up to seven years in some people after they stopped taking the pills.

Sunless tanning pills can still be found online, but these usually contain compounds like β-carotene, found in fruits and vegetables like carrots, that can turn skin an orangey shade.

Dihydroxyacetone has been approved for external use by the U.S. Food & Drug Administration for decades. But it hasn’t been cleared for use inside the body. A 2004 FDA study, however, showed that as much as 11% of the dihydroxyacetone applied to skin penetrates into living skin, and 0.5% could get into the bloodstream.

With the advent of spray tanning salons, where customers are showered with a mist of sunless tanning products, people can be exposed to aerosolized dihydroxyacetone. And these tiny droplets could be inhaled without the proper protection.

Ashlee J. Howarth, a chemistry professor at Concordia University, describes receiving a home spray tan in preparation for a wedding. The technician who sprayed the members of the bridal party didn’t offer any protective face or nose guards and didn’t wear any herself. As a chemist, Howarth was wary of exposure and found herself checking the bottle label. “I held my breath just in case,” she says.

“There’s really a lack of information about sunless tanning products,” says Natalie R. Gassman, a professor of oncologic sciences at the University of South Alabama Mitchell Cancer Institute. Gassman and others have studied the effects of dihydroxyacetone on healthy cells called melanocytes and keratinocytes, found under the dead outer layer of skin, as well as on cancerous melanoma cells. The experiments have shown that dihydroxyacetone is toxic to all three types of cells at dosage levels that people could potentially encounter through normal use (Envir. Toxicol. 2017, DOI: 10.1002/tox.22520). But estimating exposure levels is difficult because of poorly understood factors such as the amount of sunless tanner applied and how long it stays active on the skin, Gassman says.

When it comes to sunless tanning products, “No one can definitively say that they’re bad for you,” she says, adding that on the other hand, these products can help move people away from outdoor or sunlamp tanning, practices that are certainly unhealthy. But if we’re asking people to switch over to these products, Gassman says, we should understand any risks that exposure to them might pose.

This article was modified on Jan. 16, 2018, to refresh its information and data.


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