Three products for a radiant, customizable tan — without UV rays

Three products for a radiant, customizable tan — without UV rays

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Informations sur le système de pigmentation de la peau (mélanogenèse).

Melanogenesis: The Physiology of the Pigmentary System.

Carnation, pigmentation defects (brown spots), tanning… these phenomena result from the activation of a specific machinery responsible for pigment production, melanin. In this article, we take a closer look at this mechanism of the pigmentary system to help you better understand it.

The Physiological Stages Behind Melanin Synthesis.

Melanogenesis describes the complex and essential process of pigment synthesis by which melanin is produced and distributed by melanosomes in the epidermis or hair follicles. This pigment, generally black or brown, determines the color of skin, hair, and the iris of the eye.

Melanin is synthesized inside special organelles, the melanosomes, which are themselves contained within melanocytes, globular cells with numerous cellular extensions (melanocyte dendrites) that enable them to make contact with several keratinocytes up to the spinous layer (one of the layers of the epidermis). They are established at the dermal-epidermal junction, which rests on the epidermal basement membrane. The number of melanocytes varies according to the area of the body: we count around 1,000 to 1,5000 per mm2 on the body, and 2,000 or more per mm2 on the face.

Melanin is produced through a cascade of reactions:

  1. Synthesis of enzymes required for this mechanism: Among the enzymes involved in this process are tyrosinase, tyrosinase-related proteins-1 (TRP-1) and tyrosinase-related proteins-2 (TRP-2). These are proteins capable of triggering, activating and regulating the various chemical reactions leading to the synthesis of melanin pigments. They are synthesized in the rough endoplasmic reticulum (REG), then delivered to the Golgi apparatus via vesicles;

  2. Melanosome formation: Melanosomes are cytoplasmic organelles containing the enzymes formed in the previous stage. They are formed by the fusion of microvesicles. At this stage in the pigmentary system melanosomes are still unpigmented (immature) and tyrosinases are inactive;

  3. Melanin synthesis: Melanin is produced by the enzymatic transformation of tyrosine, an amino acid supplied by the bloodstream, under the action of tyrosinase. Following minor divergences in the synthesis pathway, two types of melanin pigments can be produced: eumelanins (or granular pigments) of the black to brown type, and pheomelanins (or diffuse pigments) of the yellow to reddish-brown type, with the intervention of sulfur compounds (either in the form of an amino acid, cysteine, or in the form of a tripeptide, glutathione);

    Note: In light skins, melanosomes are few 

    and often incompletely matured, 

    as well as being rapidly degraded, 

    making the skin less photo-protected and 

    therefore more exposed to solar damage 

    (sunburn), whereas in dark skins, 

    they are numerous and mature.

  4. Transfer of melanosomes from melanocytes to keratinocytes: Many melanosomes migrate from the cell body, where they are produced, to the tips of melanocyte dendrites, where they accumulate, before being transferred to the surrounding keratinocytes in the upper layers of the epidermis to ensure epidermal pigmentation and photoprotection against UV rays. Each melanocyte is in contact with around 36 keratinocytes to which melanosomes migrate;

  5. Melanosome degradation in keratinocytes: Once transferred to adjacent epidermal cells, melanosomes are then progressively eliminated with the keratinocytes as they ascend towards the skin surface.

Note: Differences in skin pigmentation 

are due to the proportion of each type of melanin 

synthesized and the size of melanosomes 

(i.e., the quantity of melanin), and not the 

numbers of melanocytes, which remain 

roughly equivalent for different skin tones.

Pigmentation: Its Biological Function.

In addition to coloring hair, eyes and skin, melanin's major physiological role is to protect the epidermis and deeper layers against external aggression, in particular UV radiation. In fact, melanin production is the body's adaptive response to prolonged exposure to the sun. It thus plays a photoprotective role.

In this way, tanning is nothing more 

than the skin's natural protection 

mechanism against UV rays.

When exposed to the sun, epidermal cells come under attack from UVA and UVB rays, which can lead to metabolic defects (aging), cell death and the development of skin cancer. To protect against UV-induced damage, the melanogenesis mechanism is triggered. The melanin produced gathers around the nucleus of keratinocytes to form a “filter” to protect DNA (genetic material) from the mutagenic and carcinogenic effects of UV.

It absorbs up to 90% of UV rays up to the visible wavelengths that pass through the stratum corneum, preventing them from penetrating the epidermis. While UVA rays are responsible for rapid, but non-persistent, pigmentation of the skin through oxidation of existing melanin, it is UVB rays that are responsible for longer-lasting tanning. Despite this photoprotection and pigmentary system, around 15% of UVB rays still manage to reach the basal layer, and 50% of UVA rays to the dermis.

Melanin also has the ability to capture 

free radicals generated within melanocytes 

and keratinocytes by UV radiation, 

thus limiting premature skin aging.

On the other hand, melanin production tends to decline with age. However, the protective effect of melanin is only valid if it is present in sufficient quantity. Thus, melanin deficiency can lead to pigmentation disorders as we age, such as vitiligo, a skin disease manifested by the appearance of white patches or lentigo or age spots. This reduction in melanin synthesis is, in fact, due to a decline in the number and activity of melanocytes, which are no longer renewed. In fact, melanocyte activity and number decline by 10-20% per decade from the age of 30 onwards.

Note: Epidermal melanocyte activity is continuous, 

while hair follicle melanocyte activity follows 

the rhythm of the hair cycle.

Biological Factors That Can Trigger This Intracellular Signalling Pathway.

A number of intrinsic and extrinsic elements can trigger the melanin production process, including :

  • UV irradiation: UV rays are well known to stimulate melanogenesis by increasing melanin synthesis and accelerating its transfer to epidermal cells. This is manifested in particular by the appearance of small, dark, round or oval mules on frequently exposed parts of the body (face, neck, back of hands, etc.), known as solar lentigo;

Sources :

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  • ORTONNE J.-P. & al. Mélanogenèse. EMC - Dermatologie-Cosmétologie (2005).

  • TOBIN D. J. & al. Hair follicle pigmentation. Journal of Investigative Dermatology (2005).

  • HEARING V. J. & al.
    Regulation of human skin pigmentation and responses to ultraviolet radiation.
    Pigment Cell & Melanoma Research (2007).

    TOBIN D. J. Human hair pigmentation - biological aspects. International Journal of Cosmetic Science (2008).

  • SCHALLREUTER K. U. & al. What are melanocytes really
    doing all day long...? Experimental Dermatology (2009).

  • TOBIN D. J. Aging of the hair follicle pigmentation system. International Journal of Trichology (2009).

  • SCHIAFFINO M. V. Signaling pathways in melanosome biogenesis and pathology.
    International Journal of Biochemistry & Cell Biology (2010).

  • HEARING V. J. Determination of melanin synthetic pathways. Journal of Investigative Dermatology

  • RAPOSO G. & al. Biogenesis of melanosomes - the chessboard of pigmentation. Medecine Sciences (2011).

  • PASSERON T. & al. Physiologie du système pigmentaire. Mélanogenèse. (2013).

  • TYMINSKA A. & al. Skin melanocytes : biology and development. Advances in Dermatology and Allergology/Postepy Dermatologii I Alergologii (2013).

  • HAMMER J. A. & al. Melanosome transfer : it is best to give and receive. Current Opinion in Cell Biology (2014).

  • PATTON E. E. & al. The melanocyte lineage in development and
    disease. Development (2015).

  • ASKARIAN-AMIRI M. E. & al. Signaling pathways in
    melanogenesis. International Journal of Molecular Sciences (2016).

  • D’ORAZIO J. A. & al. Melanocortin 1 Receptor : Structure, Function, and Regulation. Frontiers in Genetics (2016).

  • HERLYN M. & al. Crosstalk in skin : melanocytes, keratinocytes, stem cells and melanoma. Journal of Cell Communication and Signaling (2016).

  • LACHAPELLE J. M. & al. Dermatologie et infections sexuellement transmissibles. Elsevier Masson (2016).

  • PICARDO M. & al. Skin Pigmentation and Pigmentary Disorders : Focus on Epidermal/Dermal Cross-Talk.
    Annals of Dermatology (2016).

  • LEE Y. H. & al. Three streams for the mechanism of hair graying. Annals of Dermatology (2018).


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