The Chemistry of a Fake Tan: DHA, Erythrulose and How to Formulate a Streak-Free Glow

November is a funny month for tanning. In Sydney, Cape Town and Buenos Aires, summer is arriving. In London, Toronto and Seoul, the summer glow is fading fast. Either way, there's one tan dermatologists can genuinely get behind: the one that comes out of a bottle. Let's look at the clever chemistry inside.

How a self-tan works: it's (almost) baking

The active ingredient in nearly every self-tanner is dihydroxyacetone (DHA), a simple sugar. DHA reacts with amino acids in the outermost, dead layer of skin through the Maillard reaction, the same family of reactions that browns toast and roasts coffee (Braunberger et al., Journal of Drugs in Dermatology, 2018). The brown pigments formed stay in that top layer.

Two practical consequences:

• It develops over hours. Colour appears over about 2–4 hours and keeps deepening for a day or so.
• It fades in about a week, because those dead surface cells naturally shed (Canadian Dermatology Association, 2024).

The partner: erythrulose

Erythrulose is another sugar that reacts with skin in a similar way. It's usually combined with DHA rather than used alone. Suppliers describe it as developing more gradually and helping to give a more even, longer-lasting result. Our dictionary entry lists 1–3%, usually alongside DHA.

The big misconception: a fake tan is not sunscreen

A self-tan gives little to no protection against UV. The US FDA requires self-tanners without SPF to carry a warning that they don't protect against sunburn (FDA), and the Canadian Dermatology Association states plainly that self-tanners do not protect skin from the sun. Your glow still needs real sunscreen on top (and as our DIY sunscreen post explains, a properly tested one).

The rules around the world

• EU: the EU's scientific committee considers DHA safe up to 10% in self-tanning lotions and face creams (SCCS, 2020), and 10% is now the legal maximum in ready-to-use self-tanning products.
• UK: UK advisers have reviewed the same evidence (SAG-CS opinion).
• US: DHA is approved for external use only, not around the eyes, and there's no safety data for lips or mucous membranes (FDA).
• Elsewhere: check your local list. Our dictionary flags DHA as a market-specific ingredient.

Formulating a streak-free self-tan

• Use level: our DHA entry suggests 2–6% for a gradual tan and 5–10% for a deeper one (within your market's limit).
• Keep it acidic: DHA is most stable at roughly pH 3.5–5. Above that, it breaks down and can turn the formula yellow.
• Keep it cool: add DHA at the very end, below about 30 °C.
• Avoid DHA's "enemies" in the formula: amines and some amino-acid-rich ingredients react with DHA in the bottle instead of on skin. Some metal oxides can destabilise it too. Keep the base simple.
• A guide colour (a temporary bronzer or caramel tint) shows where you've applied it, which is the secret to fewer streaks.
• Package it well: opaque or airless, and keep it cool. DHA formulas have a shorter life than most lotions.
• Base ideas: a light gel with Xanthan Gum, or a lotion with Glycerin and light emollients like Caprylic/Capric Triglyceride.

Application tips for your customers

1. Exfoliate gently the day before (our exfoliant guide can help), then moisturise dry areas such as knees, elbows and ankles.
2. Apply with a mitt, in circles, using less on joints.
3. Wash palms right away.
4. Wait several hours before showering or sweating.

Explore Self-Tan Actives and Sun Care & UV Protection.