Acids in various forms have been one of the most popular groups of active ingredients in skin care products for several decades. Properly used in appropriate concentrations, acids are highly effective, multifunctional substances that brighten, hydrate and rejuvenate the skin.
When using acids, the most important thing is not to choose too strong concentration for your skin type. At concentrations that are too strong, the benefits of acids can be reversed and result in skin irritation, dryness and redness. Repeated irritation of the skin with acids that are too strong can lead to the onset of certain skin problems.
In addition to the acid’s strength, its pH will also affect how your skin reacts to it. To achieve all the benefits and exfoliating effects, a sufficient acid concentration is required, while the pH of the product must be below 4.
Acids affect the skin chemically. They improve the desquamation of dead skin cells and soften and tighten the structure of the skin. In addition, they brighten and even out the skin tone. Alongside their exfoliating effect, acids are humectants. The effect of the application of acid varies depending on the type of acid selected, and its concentration and pH.
Acids are used as an active ingredient in both leave-on and rinse-off products. Acids that are in products for daily use are usually in a liquid form, such as an essence. The concentrations of such products range from less than 3% to 7-8%, depending on the acid type selected and the type of skin for which the product is intended. Concentrations between 7-10 % can be also used every other day or couple of times in a week – daily use is not always necessary or even recommended. Concentrations that are removed from the skin typically have a concentration of 10%–25% and are not intended for daily use. Salicylic acid is an exception, as its maximum permissible concentration without a prescription is 2%. Of the alpha hydroxy acids (AHA), glycolic acid is known to be the strongest, which is why it is not used in products intended to be left on the skin in concentrations stronger than 5%.
Acids for daily use are the gentlest and this is the best way to use acids. If used daily, it is usually not necessary to apply a separate exfoliating product to the skin, except very occasionally, when, for example, the skin has been exposed to severe weather conditions for a long time causing it to become temporarily dehydrated and the stratum corneum too thick. A daily dose of acid maintains the skin’s pH balance, that is, it keeps the skin’s hydrolipidic film acidic, which creates good conditions for a balanced skin microbiome. Acidity also maintains the optimal skin moisture and the keratinization process, leaving the skin clear, moisturised, smooth and supple.
The myth that acids will make the skin thinner is not true. With ageing, the keratinization process slows down and stratum corneum, the uppermost layer of the skin, thickens. Disorders in keratinization can also occur in young skin and the stratum corneum may become thickened. AHAs normalise the keratinization process and desquamation of dead skin cells, which thins the stratum corneum if it has become too thick. This normalises the skin’s functions and makes the skin’s surface more elastic and resilient. With ageing, the lower layer of the skin, the dermis, becomes thinner, causing the skin to lose its fullness and become saggy. AHAs strengthen the dermis, that is the collagen and elastin fibers, and increase the amount of glycosaminoglycans in the intercellular matrix, which improves the moisture content of the dermis, making the skin fuller and smoother.
Different types of acids
AHAs or alpha hydroxy acids AHAs or alpha hydroxy acids are also called fruit acids. They include glycolic acid, lactic acid, amygdalic acid, malic acid, tartaric acid and citric acid. They occur naturally in fruits and berries such as sugar cane, bilberries, grapes, cranberries and apples, but are usually made synthetically. AHAs exfoliate, brighten, moisturise, soften and polish the skin, and help substances be better absorbed into the skin. AHAs should not be used on skins that suffer from rosacea, sensitive acne or perioral dermatitis.Glycolic acid
Glycolic acid has the smallest molecule size of all AHAs, which is why it is absorbed more deeply than other acids and is, therefore, more effective, but also the most easily irritating. It is one of the few substances that has been found to be absorbed all the way to the dermis. Glycolic acid is rarely used in products intended to be left on the skin in concentrations of over 5%. When using glycolic acid, the skin should be protected with a cream containing a sun protection factor. It is especially good for the treatment of wrinkles, sagging and thickened skin, and pigment spots.
Lactic acid
Lactic acid has a higher molecular weight than glycolic acid and is not absorbed quite as deeply. It moisturises and brightens the skin effectively and is also found naturally in the skin’s Natural Moisturising Factor, which is created by the keratinization Process. At concentrations of more than 5%, lactic acid acts as an exfoliating agent. It is especially good for dull, dehydrated, dry skin and mature skin
Mandelic acid
Mandelic acid has the biggest molecule size of all AHAs. It is absorbed into the skin slowly and does not irritate as easily as smaller molecular acids. Mandelic acid has antibacterial properties, unlike glycolic acid. It is especially good for acne and acne scars.
Malic acid
Malic acid has a higher molecular weight than glycolic and lactic acid, and works best in combination with other acids. It is especially good for clogged skin.
Tartaric acid
Tartaric acid is usually used in combination with other acids. It can also be used to adjust the pH of a product.
Citric acid
Citric acid is generally used to adjust the pH of a product.
BHA or beta hydroxy acid BHA or beta hydroxy acid is known as salicylic acid.Salicylic acid
Willow bark naturally contains salicylic acid, which is a BHA or beta hydroxy acid. Salicylic acid is fat-soluble, making it well-suited for oily or clogged skin and acne. It helps to clear clogged skin pores, prevents the formation of comedos and has antiseptic effects.
PHAs or polyhydroxy acids PHAs, or polyhydroxy acids, have a heavier molecular weight than glycolic acid, so do not irritate the skin as easily, but have similar effects to AHAs. PHAs exfoliate, moisturise, brighten, firm and smooth the skin, and strengthen its protective barrier. In addition, PHAs have antioxidant properties, meaning they protect the skin from free radicals.Gluconolactone
Gluconolactone is not absorbed as deeply into the skin as glycolic acid, which makes it less irritating to the skin. Gluconolactone is a multi-purpose acid due to its antioxidant and skin-barrier strengthening properties. In addition, it is suitable for sensitive and even rosacea-prone skin and with regular use can reduce the redness of the skin. It is especially good for sensitive, dull, dehydrated or dry skin, and for the treatment of wrinkles and sagging skin.
Lactobionic acid
Lactobionic acid moisturises the skin and protects it from free radicals. It is especially good for sensitive, dehydrated and dry skin.
Djusie Acid Bloom Balancing Essence contains the perfect cocktail of gentle acids for daily use in the morning and evening. The product can be applied to the skin in 1–3 layers and is also suitable for the skin around the eyes. If you have not used acids on your skin before, you should accustom your skin gradually by starting with applying one layer in the evenings. The skin may turn red and feel slightly tingly, to begin with, but this sensation will quickly subside and your skin will get used to the acids within a couple of weeks. If your skin does not react at all, you can start using the product in the mornings and evenings. Acid Bloom contains plant-based gluconolactone, which is suitable even for sensitive skin, as well as apple cider vinegar and soothing Reishi mushroom, gotu kola, betaine and xylitol. Reishi brightens the skin colour, while gotu kola enhances collagen production. Acid Bloom will make your skin glow lusciously. Acid Bloom has an acid content of 4.2% and a pH under 4.
Source: Jeffrey S. Dover & Murad Alam: Procedures in Cosmetic Dermatology: Chemical Peels