How to reduce solar lentigines?

To completely eliminate these irregularities, aesthetic medicine is particularly effective. However, there are less invasive and gentler methods to significantly reduce their appearance, such as using treatments rich in brightening active ingredients. Below is a non-exhaustive list of molecules known for their depigmenting action in skincare:

• TheAzelaic Acid :

  This dicarboxylic acid derived from cereals reduces the ability of melanocytes to produce melanin by inhibiting the enzyme tyrosinase and regulating the activity of the enzyme thioredoxin reductase. Moreover, it specifically targets pigment-loaded melanocytes or atypical melanocytes. As a result, it does not interact with healthy cells. It should be noted, however, that azelaic acid is concentrated at 20% in studies conducted on its depigmenting power, whereas in cosmetics, it is introduced at a content between 3 and 10%.

• The niacinamide

  Also known as vitamin B3, nicotinamide, or PP vitamin (Pellagra Preventive), niacinamide is part of the water-soluble B group vitamins with antioxidant, antibacterial, and anti-inflammatory properties. Regarding its anti-spot activity, it inhibits the transfer of the melanosome from melanocytes to keratinocytes. As a reminder, skin pigmentation is a complex process that begins within cells called melanocytes, which themselves contain organelles (the melanosomes) in which melanin is synthesised. There is then a transfer of these melanosomes to the surrounding keratinocytes, which will subsequently transport the pigment and possibly degrade it.

• Thearbutin acid (or alpha-arbutin):

  This refers to a molecule naturally present in several plants belonging to the Ericaceae botanical family. It can thus be extracted from the leaves of bearberry, bilberry, ash heather or even cranberry. Often referred to asnatural hydroquinonedue to itspigment regulatingcharacter, the remarkable effectiveness of arbutin acid against brown spots is due to its perfect affinity with the active site of tyrosinase, an enzyme involved in the formation of melanin. Thus, this competitive inhibition of the enzyme's active site blocks its activity, and consequently the synthesis of melanin.

• Theglycolic acid :

  This A.H.A. (alpha-hydroxy acid) is achemical exfoliant: it aids in the removal of melanin-rich skin cells on the skin's surface. This process can even stimulate cellular renewal at the basal layer of the skin, which is the deep layer of the epidermis where melanocytes, the melanin-producing cells, are located. This therefore helps todiminish brown spotscaused by ageing and sun exposure, thereby brightening the complexion.

• Theliquorice extract :

  Known by its I.N.C.I. name, "Glycyrrhiza Glabra Root Extract", liquorice extract contains 95% of glabridin, a compound that operates at several levels to regulate the phenomenon of hyperpigmentation. It significantly reduces the amount of endothelin-1 (a mediator involved in the pigmentation process) released by keratinocytes after exposure to UV rays. Additionally, it inhibits the activity of phospholipase A2 (PLA2), an enzyme released by epidermal keratinocytes after exposure to UV rays or during inflammation, which stimulates tyrosinase activity and thus melanogenesis. Other active compounds, such as glabrene, isoliquiritigenin licuraside, isoliquiritin, and licochalcone A, isolated from liquorice extracts, have also demonstrated tyrosinase inhibitory activity.

• Thetranexamic acid :

  Thissynthetic derivative of lysine, an amino acid present in the skin, acts on skin hyperpigmentation byblocking the interaction between skin cells and melanocytes, thus limiting the synthesis of melanin.Tranexamic acid then visibly reduces skin colour irregularities and improves complexion uniformity.

Solar lentigines are often sensitive to friction. They may start to peel or bleed. To remove them, a dermatologist may resort to liquid nitrogen, which is applied directly to the brown spot. This method is accompanied by a burning sensation and the skin may appear red and swollen. However, within about ten days, the healing will be done and the sun spot will have disappeared. This method is very effective on light phototypes. However, on darker skin, there is a risk of residual halo hyperpigmentation.

Furthermore, other methods exist such as laser radiation, flash lamp, or even chemical peeling. It is up to the dermatologist to assess which method is most suitable.

• LOWE N. J. & al. Azelaic acid 20% cream in the treatment of facial hyperpigmentation in darker-skinned patients. Clinical Therapeutics (1998).

• GAO J. & al. The use of botanical extracts as topical skin-lightening agents for the improvement of skin pigmentation disorders. Journal of Investigative Dermatology Symposium Proceedings (2008).

• CHANG T. S. An updated review of tyrosinase inhibitors. International Journal of Molecular Sciences (2009).

• SARKAR R. & al. Cosmeceuticals for hyperpigmentation: what is available ? Journal of Cutaneous and Aesthetic Surgery (2013).

• MOHAMMADAMINI H. & al. A comprehensive review of the therapeutic potential of alpha-arbutin. Phytotherapy Research (2021).