PIGMENTATION ON BLACK & DARK SKIN

Synthesis of pigments: 

Melanogenesis is the scientific term regarding skin pigmentation. It’s development takes place within the epidermis, on the uppermost layer of the skin, within specific dendritic cells known as melanocytes. These melanocytes interact with the adjacent keratinocytes to diffuse the synthesised melanin evenly. The melanogenesis process takes place within specific organelles called melanosomes, which are intrinsic to melanocytes. It is therefore the support of the synthesis of different pigments (melanins), which is responsible for our specific skin colour (phototypes).

Physiology of the skin

The skin represents around 15% of the body weight in adults and has a surface area of around 1.5 to 2m². The skin is the largest organ in the human body. Its principal role is to function as a physical barrier to protect us from mechanical, chemical, physical or even microbiological attacks. It also possesses sensory properties (touch, pressure...), temperature regulating properties (blood flow modulation), metabolic properties (synthesis of vitamin D, energy reserves...), immune properties, and a unique defense system against UV rays, known as pigmentation.

The pigmentation process: melanogenesis

The melanogenesis which is responsible for pigmentation is a response to an exterior stimulus: ultra-violet rays (UVs). We talk of light-induced pigmentation, more commonly known as “tanning”. This is different from constitutive or basal pigmentation, which is specific to an individual. By synthesising melanin, the skin protects us from physico-chemical attacks, thus reducing the penetration of UV rays (Fig. 4). This mechanism is also known as natural photo-protection.

Figure 4: Diagram of the cutaneous penetration of UV rays

As we have seen previously, the main basis of melanogenesis is the melanosome, the specific organelle of melanocytes. The melanosome is the support in which development and depositing of the melanin is carried out. The melanin grains are vehicles, via membrane proteins, leading to the extremities of each melanocyte dendrite, to transfer their content into the adjacent keratinocytes in order to dissipate the colour evenly. We have also seen that the number of melanocytes is not the cause of interethnic variations since this number is the same whatever the colour of the individuals skin. It is therefore essential to detail the melanogenesis mechanism in order to understand how it works and regulates, as well as how it is able to act better to regulate.

The melanogenesis process is a complex biochemical mechanism which implicates a number of enzymes, such as tyrosinase, TYRP-1 and dopachrome tautomerase (TYRP-2). (Fig.5). All of these play a fundamental role in the synthesis of melanin and allow pigmentation to be regulated.

Tyrosinase (or DHI oxidase) :

• melanogenesis limiting enzyme
• catalyses the first reactions of the process
• also catalyses the formation of indole-5,6-quinone compound via DHI
• is necessary for the transformation of DHICA in indole-5,6-quinone-2-carboxylic acid compound by TYRP-1

TYRP-1 or DHICA-oxidase:

• Catalyses the oxidisation reaction of the DHICA in indole-5,6-quinone-2-carboxylic acid compound
• Functions in synergy with tyrosinase
• Stabalises the Tyrosinase

Dopachrome tautomerase or TYRP-2:

• Catalyses the formation of DHICA via Dopachrome

CONCLUSION

Melanogenesis is a complicated process to modify because it is genetically programmed, but it can be modulated. For black and dark skin, this mechanism races ahead very quickly, which could be the cause of a mottled and uneven skin tone. This is the case for hyperpigmentation, which is the most common reason for most visits to dermatologists. The MEL’OYA^® range was developed specifically to provide an effective solution to the problem of hyperpigmentation and unification of the complexion.