How do they act?
Exfoliating the skin or carrying out a chemical peeling means applying to the skin substances with an exfoliating action, which aim at the partial removal of portions of the epidermis or dermis with subsequent stimulation of cell turnover (renewal).
In hyperpigmentation defects this practice can be useful mainly for two reasons:
- by accelerating the exchange of cells at the epidermal level, the loss of melanin from the stratum corneum is increased and the transfer of the melanosomes to the keratinocytes is decreased;
- the absorption of other active substances with depigmenting action is facilitated.
Types of Chemical Peeling
Chemical peels are divided into two categories: those for cosmetic use and those for dermatological use; this distinction is made based on the depth of penetration of the assets and on the basis of the effect to be obtained. Among the most important assets belonging to this category can be found:
- Alpha and beta hydroxy acids
- Retinoic Acid
- Trichloroacetic acid
Alpha and beta hydroxy acids
They are also called "fruit acids" because they are present in high concentrations in grapes, apples and other vegetables. Chemically, they are organic acids made up of an alcoholic group located near the terminal carboxylic group, a characteristic that gives the molecules a high acidity, greater than that of common organic acids.
At epidermal level, the main effect of the application of alpha and beta hydroxy acids is the decrease in the cohesion of the corneocytes, with consequent desquamation and increased cell turnover. Newly synthesized keratinocytes are less rich in pigments. They can have side effects like redness, dermatitis and sensitization. These effects disappear when applications are suspended.
Glycolic acid
Glycolic Acid is one of the most used compounds, since among all the analogues it is the one that expounds the fastest action and, thanks to the reduced molecular weight, it easily penetrates into the stratum corneum. Its activity is linked to the ability to reduce the forces of cohesion between the corneocytes by direct action on desmosomes (protein junctions between adjacent epithelial cells). Used in cosmetics at concentrations between 10% and 15%, it causes a progressive exfoliation of the skin. Products containing doses of glycolic acid between 50% and 70%, adequately buffered, are instead restricted to dermatological use.
Lactic acid
Lactic acid is effective in cases of hyperpigmentation related to skin aging, photoageing, pregnancy, use of birth control pills and post-inflammatory hypermelanic spots.
Salicylic acid
Salicylic acid is a beta-hydroxy acid that presents a selective keratolytic action on the protein chains of keratin present in the corneocytes. It has no effects on other proteins and is therefore well tolerated by the underlying cells that do not contain keratin. It shows a good exfoliating and smoothing action even at low concentrations (1-2%) and is particularly effective in the treatment of post-inflammatory hyperpigmentation and melasma1
Retinoic acid
Retinoic Acid is the acid form of vitamin A.
Treatment with products based on retinoic acid and its derivatives causes a marked exfoliation of the epidermis and the production of mucous glycoproteins, more elastic than keratin, which contribute to soften the stratum corneum. It is generally used in the ambulatory setting in association with depigmenting active ingredients.
Retinoic acid, also known as tretinoin in its trans form, is used in dermatology in concentrations ranging from 0.05% to 1% in the treatment of post-inflammatory hyperpigmentation. The use of this active ingredient takes a very long time and the effects begin to be noticed after about 24 weeks.
Retinoic acid cannot be used in cosmetics, where it is possible to use only vitamin A and its derivatives that are transformed into retinoic acid in vivo.
Trichloroacetic acid
Trichloroacetic acid is used, like retinoids, only in dermatology. It can be used in concentrations ranging from 10% to 40%, to achieve superficial peelings or those arriving at the level of the papillary dermis or deep reticular. For the treatment of hypermelanoses, trichloroacetic acid is used at a concentration of about 20%. Applied on the skin, it produces a very evident inflammation that manifests itself with redness, swelling and production of serum which, by drying, forms crusts. The skin regenerates within 10-15 days.
