An even skin tone is usually associated with healthy skin. In contrast, skin subject to premature aging caused by UV light (photoaging) experiences an increase in the production of melanin, the pigment controlling skin colour. And this results in the appearance of skin spots.
History and origins
In ancient Egypt, as well as in later Roman civilisations, white skin was believed to represent wealth. Already at that time, there was a wide range of remedies to combat sunspots and freckles, among others. Later on, in the Far East, it became fashionable in Japan to apply rice powder to white skin as a sign of beauty.
Nowadays, far from being related to social status, we are certain that prolonged sun exposure causes premature skin aging. It is also a major risk factor for skin cancer and other conditions. This is why the main cosmetic treatments focus on protecting the skin from damage caused by sun exposure, as well as aiming to reduce tanning and the appearance of aging skin, with the use of depigmenting actives for the skin.
Why do I have dark spots on my skin?
The spots are caused by an accumulation of melanin pigment expressed in the keratinocytes, the cells of the most superficial layer of the epidermis, the stratum corneum. The main function of melanin is to protect the keratinocytes and thus prevent the skin from alterations and premature aging. Melanin pigments are formed from a biochemical reaction, Tyrosine – L-DOPA – Melanin, by the enzyme tyrosinase. This reaction takes place in cells specialised in melanin production, the melanocytes. Melanocytes are located in the basal layer of the epidermis and transport melanin to the keratinocytes via vesicles called melanosomes.
There are two types of melanin: Eumelanin, a black pigment and the majority in dark phototypes, and Pheomelanin, a red pigment and the majority in light phototypes.
The level of pigmentation of the skin depends mainly on the activity of the melanocytes and the amount of melanin they produce.
Factors increasing the predisposition to spot formation
The appearance of hyperpigmentation in the skin is fundamentally caused by abundant and continuous sun exposure over time. In addition, some factors such as genetic predisposition, stress and hormonal changes, accelerate photoaging of the skin with the consequent appearance of hyperpigmentation and an increase in the thickness of the stratum corneum of the epidermis.
In addition, hormonal changes or a prolonged rise in Cortisol hormone, which occurs in stressful situations, activates Melanocyte Stimulating Hormone (MSH), which activates the synthesis of Melanosomes in Melanocytes.
Depigmenting agents for the skin to prevent spots from appearing at an early age
The main way to prevent hyperpigmentation in the skin is the use of photoprotection. Cosmetic products with a sun protection factor (SPF), whether they are formulated with chemical or physical filters, are the most effective products in preventing hyperpigmentation.
Antioxidant ingredients such as Vitamin C or other derivatives decrease the formation of free radicals that cause stress responses, among others. Therefore, the use of antioxidants keeps under control the formation of melanin-containing melanosomes.
Cosmetic ingredients to prevent an increase in the appearance of new spots once they have appeared
Active ingredients that inhibit the action of the enzyme tyrosinase are the most common skin depigmenting agents. By inhibiting this enzyme, the formation of Melanin is suppressed. In cases where there is an overexpression of Melanin, suppressing the formation of the pigment is one of the most effective options. Active ingredients that act in this way are: tranexamic acid, kojic acid, azelaic acid and retinoic acid.
Some depigmenting active ingredients for the skin also act by inhibiting the transport of melanosomes, thus preventing the melanin formed from reaching the keratinocytes and expressing itself in the form of a spot. This is the case with: Niacinamide or Arbutin.
Depigmenting agents for the skin that reduce spots that have already appeared
The skin renews itself approximately every 28 days, which is when the cells of the stratum corneum of the epidermis are shed and make way for new cells. Some cosmetic ingredients increase the rate of cell renewal in order to improve skin quality, as is the case with chemical exfoliants.
Hydroxy acids are the chemical exfoliants par excellence. They are divided into two subfamilies: alpha hydroxy acids, such as glycolic acid, mandelic acid, lactic, citric or tartaric acid, or beta hydroxy acids, such as salicylic or succinic acid. They are corneodesmolytic ingredients, as they break the bonds between keratinocytes, the desmosomes. In this way, the hydroxy acids accelerate the detachment of keratinocytes, which are loaded with melanin, and thus promote skin renewal.
Other chemical exfoliants are polyhydroxy acids such as Gluconolactone, which act in the same way but as being larger molecules they penetrate less into the skin and are better tolerated by sensitive skin.
Synergies between depigmenting ingredients for the skin
Depigmenting agents, like many cosmetic active ingredients, increase their efficacy when used in combination with others. One of the most commonly found combinations among cosmetic formulations is that of chemical exfoliating ingredients together with classical tyrosinase inhibitors, for example: kojic acid + glycolic acid or azelaic acid + glycolic acid.
Combinations of strong antioxidants with other depigmenting agents are also often used, such as tranexamic acid + vitamin C + niacinamide, or tranexamic acid + kojic acid, which establishes a good synergy of depigmenting action.