If we review history a bit, we realize that they are nothing new. Already in ancient Egypt, Cleopatra used sour milk, now known to contain lactic acid, while French women used aged wine containing tartaric acid. Personally, I find acid exfoliants very aggressive for the skin, and their effects can be achieved through other means, but since they are very popular and you have asked for my opinion a lot (thank you for your trust), I have prepared a quick guide with their properties, dosage, and recommendations.
HOW THEY WORK
These are acidic substances that alter the skin's pH, or the balance between its acidity and alkalinity, lowering it to levels below normal. This action causes a breakdown of the cellular interconnections of corneocytes (mature cells), releasing them and accelerating their elimination. As a result, the basal layer of the skin accelerates the tissue renewal process.
CITRIC ACID
It is found in food, especially in citrus fruits. Lemons are particularly rich in this acid and contain up to 8% by weight of dry matter. This means that every liter of squeezed lemon contains up to 47g of citric acid. Its action is mainly keratolytic.
GLYCOLIC ACID
It is obtained from natural sources such as fruits, beets, and sugarcane. The exfoliation produced is usually very superficial, and even without removing the product, the probability of irritating reactions is relatively low. As for acid exfoliants for the skin, this one provides very rapid exfoliation (light molecule, low molecular weight, easily absorbed by the skin).
Its cosmetic use:
- Glycolic acid stimulates the synthesis of collagen, hyaluronic acid, and mucopolysaccharides.
- Excellent exfoliating properties at a concentration between 10% and 15%: indicated for the treatment of acne, psoriasis, and keratosis.
- At a higher concentration (15-70%), this exfoliating substance is used to treat wrinkles, stretch marks, and hyperpigmentation.
Common side effects after application:
Redness, dermatitis, tingling, erythema, and skin sensitization.
GLUCONOLACTONE
It releases gluconic acid, promotes exfoliation and cell renewal, modulating the keratinization process. It also has good antioxidant and restorative capabilities for damaged skin barrier. It is an exfoliant with excellent moisturizing properties and, being naturally present in the skin, helps with cell renewal. Much gentler than hydroxy acids and is often combined with other exfoliating substances (particularly Alpha-hydroxy acids) to reduce possible irritating phenomena that might be observed on the skin after its application.
LACTIC ACID
Lactic acid has very similar properties to glycolic acid, in addition to lower cost and greater dermal compatibility. It is one of the acid exfoliants for the skin that naturally acidifies the surface of the epidermis. However, it did not achieve the commercial success of glycolic acid, with which it is normally associated in many cosmetic products. It provides softness, hydration, luminosity, and elasticity to the skin, but more in-depth study is needed to confirm that it is capable of stimulating ceramide synthesis, and thus increasing the skin's barrier function.
Its cosmetic use:
- Indicated as an exfoliating agent in the treatment of dandruff, keratosis, warts, calluses, and acne.
- It is combined with other exfoliating agents to counteract dry and arid skin.
- It is also used in feminine hygiene products.
Common side effects after application:
Redness, dermatitis, and skin sensitization.
LACTOBIONIC ACID
This acid is formed by combining gluconic acid, a polyhydroxy acid, and a sugar molecule (galactose). Due to its relatively high mass and the way it reacts with moisture, it acts more on the skin's surface and can only induce very mild exfoliation.
Its cosmetic use:
- Notable reparative and healing activity, typical of galactose, a sugar that plays a key role in collagen synthesis and aggregation and in cell migration phenomena.
- It has a very powerful antioxidant action and remarkable reparative activity.
- Brightens and softens the skin. It is much gentler than hydroxy acid exfoliants.
- Promotes cell renewal by regulating keratinization mechanisms.
- Exfoliant indicated in the treatment against skin aging.
- Given its delicate action, it is used in the treatment of sensitive skin.
MALIC ACID
It is an alpha-hydroxy acid that comes from fruit and is found in greater quantities in apples. Combined with other AHAs, it exerts good keratolytic activity – it decreases adhesion between mature cells and reduces the thickness of the stratum corneum, facilitating the rapid elimination of pigmented cells, increasing skin luminosity thanks to this depigmenting effect. Applied to acne-prone skin, it exerts a comedolytic activity, so it works well to treat skin with cysts and microcysts.
MANDELIC ACID
Mandelic acid was first used in cosmetics about fifty years ago, and it generated a lot of attention in the world of acid exfoliants for the skin. So much so that, today, it is one of the most used ingredients to lighten and exfoliate the skin. The name "mandelic" derives from the word "mandel" which means almond in German.
For me, it is an acid between glycolic and salicylic (stronger than glycolic but not as strong as salicylic). In most cases, immediately after applying the product to healthy skin, the client does not feel burning, tingling, or pain, so it is the one I recommend for more sensitive skin. This chemical exfoliant can also be applied a few hours before sun exposure since the substance is not photosensitizing.
Its cosmetic use:
- It is mainly indicated in the treatment of acne.
- Also indicated to treat blackheads, skin discolorations, dry and arid skin, superficial wrinkles, rosacea.
PYRUVIC ACID
It is much stronger than glycolic and salicylic acid.
Its cosmetic use:
- Powerful keratolytic activity, effective for the treatment of skin imperfections.
- Rapid elimination of pigmented cells, increasing skin luminosity thanks to this depigmenting effect.
- Thanks to its lipophilicity, it can penetrate deeply into the follicle where it exerts bacteriostatic and comedolytic activity, facilitating the emptying of cysts and microcysts.
- It also has a sebostatic action.
RETINOIC ACID
(Retinol derivative) Acid form of vitamin A. The exfoliating action of retinoic acid is favored by the skin's reparative and normalizing capacity. However, like tretinoin, retinoic acid is a known teratogen at high doses, even long after the end of treatment. Its use is prohibited during pregnancy and lactation.
Its cosmetic use:
- Promotes cell renewal, hydrates the skin, and keeps it soft for longer.
- This exfoliant is usually formulated together with depigmenting active ingredients.
- It has a good effect in minimizing fine lines.
- Promotes the maintenance of skin integrity and functionality.
SALICYLIC ACID
It is a beta-hydroxy acid derived from the enzymatic hydrolysis of salicin, a salicoside glycoside extracted from the Salix alba (willow) plant. Of all the acid exfoliants for the skin described above, this is a much stronger acid. It is soluble in oil and skin lipids, which means it can easily penetrate the stratum corneum and the inside of the sebaceous ducts. Thanks to its structure, it is also a good antimicrobial.
Its cosmetic use:
- Used in cosmetics to prepare superficial peels in the treatment of mild to moderate pustular acne.
- The exfoliant quickly penetrates inflamed lesions, exerting a bacteriostatic and soothing action.
- Guaranteed exfoliating effect even at very low concentrations (1-2%).
- Indicated in the treatment of melasma and post-inflammatory hyperpigmentation.
- Throughout the entire treatment period (4-6 sessions, separated by at least 3 weeks), it is strongly recommended not to expose oneself to the sun.
Common side effects after application:
The exfoliating effect can be very evident: possible formation of dark spots (spontaneously reversible effect in a few days). It should not be administered to patients allergic to salicylates.
TARTARIC ACID
Tartaric acid is an alpha-hydroxy acid found in fruit and is particularly abundant in grapes and tamarind. It is used for the formulation of depigmenting products, designed to treat melasma. It is also used in anti-acne, anti-aging products, and in the treatment of impure, asphyxiated, and thickened skin. Another notable property is its ability to regulate skin pH. It is generally used in concentrations between 1% and 10%, alone or in combination with other alpha-hydroxy acids.
TRETINOIN
(Retinol derivative) Used in dermatology as an exfoliant, in the treatment of post-inflammatory hyperpigmentation. It is usually used in very low concentrations (0.05-1%). Its effects are visible in the long term (after 6 months of treatment).
TRICHLOROACETIC ACID (TCA)
Used only in dermatology for the treatment of: warts, skin discolorations, post-acne and post-surgical scars, rosacea, moderate-to-severe photoaging, melasma, sun spots, keratosis.
It is used in concentrations ranging from 10% to 40% depending on the type of peel to be performed (10-25% for a superficial peel, 30-40% for a deep peel). Depending on the concentration used, the skin takes 3 to 15 days to regenerate. After treatment, stinging, burning, hyperemia, redness, swelling, and erythema may occur.
