The various self-tanning substances used for a sun-kissed complexion without sun exposure.

The dihydroxyacetone, also known as DHA, is an ingredient of synthetic or plant origin. The naturally derived ingredient is typically obtained through a biotechnological process that involves stages of fermentation and bacterial bioconversion of glycerol extracted from corn or sugarcane. DHA is the molecule most commonly found in self-tanners due to its effectiveness. When DHA is applied to the skin, it reacts upon contact with the amine functions carried by the amino acids present in the dead cells of the corneal layer to form pigments: the melanoidins. The browning effect of the skin results from this reaction, called the Maillard reaction and presented below.

Melanoidins should not be confused with melanin. The former are artificial polymeric pigments formed in the stratum corneum, while the latter are natural epidermal polymeric pigments produced during the process of melanogenesis.

It's worth noting that the more corneocytes there are, the more intense the brown colouration becomes, hence the appearance of sometimes darker areas on the thicker parts of the skin, such as the knees, elbows or heels. That's why it's generally recommended to exfoliate before using a self-tanner. DHA allows for a tanned complexion to be achieved in about six hours. The intensity of the colouration increases proportionally with the concentration of DHA, the temperature and the pH of the skin and the product, an alkaline environment favouring the Maillard reaction. The browning then gradually disappears as the cells of the horny layer are renewed.

Erythrulose is a natural ketonic sugar, notably found in red fruits. Like DHA, it is capable of combining with the amino acids in the corneal layer to form melanoidins. However, when used alone, erythrulose is unable to provide an intense colouration of the skin. This is why it is generally combined with DHA. This combination also allows for a more even and longer-lasting tan, due to a better dispersion of pigments in the corneal layer. Indeed, erythrulose is more stable than DHA and has a slower reaction rate. Thus, erythrulose colours the skin more slowly. This is also the reason why the combination of these molecules promotes the achievement of a natural and progressive sun-kissed complexion.

At Typology, we combine dihydroxyacetone and erythrulose in our self-tanning products.

Troxerutin is a semi-synthetic flavonoid derived from rutin, a natural polyphenol found in certain plants such as eucalyptus, or hawthorn. It is primarily used in pharmacology for its vasoprotective effects in the treatment of venous insufficiency, but it also has relevance in cosmetics when it is combined with dihydroxyacetone. Indeed, although the application of troxerutin alone does not generate any colouration, its combination with DHA allows for the intensification and stabilisation of the tanning effect.

Furthermore, at a concentration of 3%, troxerutin also possesses antioxidant and anti-inflammatory properties. Indeed, it is capable of trapping free radicals due to its chemical structure rich in double bonds, as well as inhibiting the release of certain pro-inflammatory cytokines. Troxerutin thus promotes the maintenance of the integrity of the skin barrier function and the achievement of a uniform and luminous complexion.

Less known to consumers than DHA and erythrulose, troxerutin has also been less studied as a self-tanning molecule, which explains its more limited use in products of this type.

The Isochrysis galbana is a unicellular microalgae primarily cultivated for aquaculture. However, it is also considered by the cosmetic industry for its self-tanning properties, which are derived from its richness in dihydroxyacetone. The addition of extracts from Isochrysis galbana in self-tanning products could indeed increase the concentration of DHA, thereby optimising the colouring effect. However, to confirm its effectiveness and safety in this context, scientific studies are necessary.

On the other hand, recent studies have suggested that extracts of Isochrysis galbana could play a role as a pigmentation accelerator. They contain pheophorbides, which are degradation products of chlorophyll, and possess photosensitising properties. Theoretically, these compounds could promote faster tanning under the effect of UV rays. However, the use of photosensitising substances is not without risk. These molecules not only promote skin tanning, but also increase the risks of sunburn, hyperpigmentation, and even skin cancer. Furthermore, this approach deviates from the principle of self-tanners, which aim to induce tanning without sun exposure.

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• PENCREAC’H G. & al. Les microalgues marines : source alternative d’acide eicosapentaènoïque (EPA) et d’acide docosahexaènoïque (DHA). Oléagineux, Corps Gras, Lipides (2004).

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• CIRIMINNA R. & al. Dihydroxyacetone: An updated insight into an important bioproduct. ChemistryOpen (2018).