Every summer, the same scene: someone slathers on self-tanner to look like they're back from holiday, and wakes up the next morning with a strange orange shade more like a carrot than a tan. It's not magic, and it's not bad luck - behind it is concrete chemistry, and once you understand it, the mistake is easy to avoid.

The active ingredient in almost all self-tanners is DHA (dihydroxyacetone). According to one cosmetologist, it reacts with the amino acids in the skin's surface layer through the so-called Maillard reaction - the same one that makes bread brown when baking - creating brown pigments. The color develops gradually, between 4 and 24 hours, and lasts until the skin naturally renews itself, usually five to seven days.

So why does it sometimes come out orange? The culprit is a few factors: too high a concentration of DHA, especially on fair skin; a poor-quality formula; and the most common mistake - uneven application on dry skin or where there are old, flaking cells. The product "grabs" more strongly in those spots, and that's where the blotches come from.

The solution is in the preparation, not the product. Exfoliate the skin gently a day or two earlier, but not right before applying. Avoid retinoids and strong acids before use, and make sure the skin is well hydrated. Apply evenly, to all areas equally. And finally - not every self-tanner is the same: the good ones combine DHA with hydrating ingredients and pH regulators. A tan without the sun is possible; it just takes a bit more care than the ads admit.