How can we tan without UV?

Tanning is often perceived as a lovely glow that the skin acquires after sunbathing. From a biological perspective, it is actually a skin defence mechanism against the assault of UV rays. Indeed, these generate free radicals, unstable species that damage our cell membranes, but also our DNA, which can lead to mutations and the formation of cancerous cells. Free radicals can also cause the denaturation and loss of function of fibrous proteins such as collagen and elastin, structural proteins of the dermis. To protect itself, the skin responds by activating melanogenesis, the process of synthesising melanin, the brown pigment responsible for tanning. However, this does not provide complete skin protection and needs to be supplemented by the application of a broad-spectrum sunscreen.

In recent years, there has been an increasing number ofself-tanning products appearing on the cosmetic care market. Mousse, cream, gel, serum... these products offer several benefits, including the ability to achieve a beautiful sun-kissed complexion without having to expose oneself to the dangers of UV rays.

Most self-tanning products contain a plant-derived molecule, known as dihydroxyacetone (DHA). Once applied to the skin, this compound induces a brownish hue within 4 to 6 hours, by reacting with the amino acids in the stratum corneum layer of the epidermis through a Maillard reaction to form pigments, the melanoidins, which are responsible for skin colouration.

We also frequently encountererythrulose in self-tanning products, a sugar found in red fruits. This compound acts similarly to DHA but more slowly. TheDHA-erythrulose combination allows for a more natural and uniform tan. Moreover, erythrulose has moisturising properties that counterbalance the drying power of DHA.

At Typology, we have developed two self-tanning formulations, providing a natural bronzed complexion. For a natural and gradual tan, you can try our self-tanning serum. It is concentrated at 10% in DHA and also contains carob pulp (INCI: Ceratonia Siliqua Seed Extract), a compound rich in inositol, a molecule that acts on melanogenesis. We also recommend our self-tanning gel for the body, enriched with 6% DHA. This care product also includes aloe vera, which is highly moisturising.

Note : there are also self-tanning showers, which are booths where fine droplets of a self-tanning lotion are sprayed onto the body and/or face. This is a fairly convenient and quick technique (less than ten minutes if a machine is used) offering a uniform result. However, one might question the risk of inhaling DHA. Indeed, the ingestion or inhalation of this molecule could potentially lead to asthma, lung diseases or cancer. To date, no health authority has established that self-tanning showers pose a health risk, due to the short exposure time to the product.

To achieve a natural sun-kissed complexion that is lighter than what you would get from using a self-tanner, you can turn to "healthy glow" treatments. These contain targeted active ingredients, often acting on the process of melanogenesis. For instance, consider the carrot macerate.

This vegetable oil has a slight colouration, which allows it to impart a healthy glow. Moreover, due to its high content of vitamin A and carotenoids, this active ingredient is an excellent antioxidant, helping to protect the skin against free radicals. It also has a stimulating effect on melanogenesis. Other vegetable oils, such as the buriti oil , also have a slightly orange hue, providing a subtle tan.

To promote melanogenesis, you can also rely oncarob pulp extract. Containing inositol, this ingredient acts on the diacylglycerol/protein kinase C (DAG/PKC) biological pathway. This mechanism triggers a cascade of reactions, ultimately leading to theactivation of tyrosinase, the key enzyme in melanogenesis. Theglycyrrhetinic acid, the active principle of liquorice, serves as an alternative to carob pulp extract and acts similarly on this biological pathway.

To achieve a tan without UV exposure, one can also modify their diet. Indeed, consuming certain foods, rich in specific nutrients, can promote a tanned appearance. Similarly to topical treatments, the most well-known ally is beta-carotene. This is converted into retinol, the active form of vitamin A, in the intestinal lining.

Indeed, the presence of retinol in the blood stimulates melanogenesis, the synthesis of melanin. Beta-carotene is found in many fruits and vegetables, such as carrots, tomatoes, melons, apricots, peaches, mangoes, broccoli, and spinach. Whether in a cold soup, a summer salad, or a juice, don't hesitate to include them in your meals. The consumption of eggs is also recommended, as they are rich in vitamin A.

You can also turn to dietary supplements rich in beta-carotenes. They have the advantage of containing a higher concentration of beta-carotenes than traditional foods, which optimises tanning. The initial effects of self-tanning capsules often appear after a month. It's also worth noting that the ideal duration of a course is generally three months.

• ZUCCA A. & al. A narrative review of the potential for self-tanning products to replace sunbed use among individuals desiring a tanned look. Photodermatology, Photoimmunology and Photomedicine (2014).