Exfoliating Acids

Acids: an essential overview

Acids and acid-based products are the cornerstone of modern skincare: the incredibly effective workhorse of every skin’s essential routine. But no two acids should ever be considered the same, and knowing what to use and when is paramount. At Skinesis we currently most favour lactic acid, salicylic acid and mandelic acid, both in our treatments and in our products.

Chemical exfoliation conducted via any of these acids leaves skin not only smoother and more even in appearance, because the skin’s own regeneration process can happen more efficiently, but also leaves it more receptive to products applied subsequently, allowing greater penetration and far improved efficacy. Thus, knowing how and why to use the acids is as important as knowing what to use.

For any formula that is applied to the skin topically to be effective it must be able to penetrate into the skin where it can act upon living cells, a property known as bioavailability. The bioavailability of an acid is key: a greater bioavailability means deeper, more noticeable, dermal effects. Acids, including lactic acid particularly, have been shown to trigger the increased production of mucopolysaccharides, the long, unbranched chain amino sugar repeating units with lubricant properties, also known as glycosaminoglycans (GAGs), and collagen, the structural protein that is one of the building blocks of the skin’s support network and which is responsible for skin thickness and resilience. Crucially, bioavailability is enhanced primarily by small molecular size, one of the most important factors in a formula’s ability to penetrate the top layer of skin, the epidermis.

We know that fine lines, wrinkles and even some scars can be reduced in appearance with the regular use of acids for chemical exfoliation. How is this accomplished? When new layers of skin grow they follow a ‘template’ of the skin above. By removing the top layers of skin regularly, the scar ‘template’ is reduced and therefore so the scar will become less visible over time.

Lactic acid and mandelic acid are both alpha hydroxyl acids (AHAs), which have an important effect on keratinisation, detectable clinically by the formation of a new stratum corneum (outermost layer of the epidermis), the top layer of our skin. AHAs appear to modify this formation by encouraging diminished cellular cohesion, weakening intercellular bonding, between corneocytes, the predominant cell found in the stratum corneum, at the lowest levels of the stratum corneum. By dissolving this ‘glue’ that holds the dead skin cells together the process of cellular renewal is reinforced and skin becomes smoother and more even in tone and texture. By the same principle, AHAs are effective for acneic skin because by clearing the dead skin cells the potential congestion is limited, in turn is boosted by the achievement of greater cellular renewal. A point of interest here is that conversely, this corneocyte cohesion and intercellular bonding is strengthened by any dehydration occurring in the skin as the skin makes attempts to retain water levels.

Lactic acid (as its name suggests, sometimes deriving from sour milk) is often favoured for treatment of ageing skin and pigmentation. The human body produces lactic acid to maintain its optimal pH balance and it also plays a role in the body’s immune defence. Like other acids, lactic acid will exfoliate the outer surface of the skin and encourage turnover of new cells. But it is also a natural humectant, attracting moisture from the collagen levels and drawing them up to the skin surface – which makes it particularly good for dry, dehydrated and sun-damaged skin as well as acne and fine lines and wrinkles. Further, lactic acid stimulates the skin to produce more collagen and has the benefit of being milder in formulation than other AHAs. When used at concentrations of 2% or less, lactic acid is pH-regulating, antimicrobial, and humectant. When used at concentrations higher than 2%, lactic acid will perform those same functions as well as offering enhanced brightening, improved collagen synthesis and increased exfoliation.

Mandelic acid, originally derived from bitter almonds, is also an AHA. It penetrates the skin to a lesser extent than some other acids (for instance, glycolic acid) and is therefore frequently considered more gentle. Like other acids it works to accelerate cellular turnover by dissolving the intercellular bonds between skin cells and also strengthens collagen. Mandelic acid often appears in higher concentration but it is a gentler AHA than most due to its lower level of penetration and is often used for sensitive skin and rosacea. Its antibacterial properties make it appropriate for acne treatment and at certain concentrations it also has the ability to exfoliate without brightening, which is preferable for some skin tones.

Salicylic acid is the third type of acid that we favour at Skinesis. It is an important active metabolite of aspirin (acetylsalicylic acid), in part a prodrug to salicylic acid, and is often best known for its use in the treatment of acne. Salicylic acid is a lipophilic monohydroxybenzoic acid, a type of phenolic acid and a beta hydroxyl acid (BHA). BHAs work slightly differently to AHAs: their lipophilic nature means that they are oil-soluble and can therefore penetrate deeper than AHAs, making it a highly effective exfoliant which performs deep within the pores as well as on the skin’s surface and is thus especially appropriate for acneic and oilier skin.

Like other acids, salicylic is keratolytic (it breaks down the skin’s keratin) and dissolves the intercellular bonds discussed earlier, but to slightly different effect in acneic skin: as well as smoothing fine lines and the general appearance of skin, pores are protected from further congestion that leads to breakouts. It also has powerful anti-inflammatory properties and helps to calm skin, and has the ability to reduce sebum secretion.

Further reading and research

Cochrane Database Syst. Rev. 2005 Jan 25;(1):CD001782.
Interventions for photodamaged skin
M Samuel, RC Brooke et al.

Journal of the American Academy of Dermatology. 1984 Nov;11(5 Pt 1):867-79.
Hyperkeratinization, corneocyte cohesion, and alpha hydroxy acids
Van Scott EJ, Yu RJ.

Int. Journal of Fertility and Women’s Med. 1999 Mar-Apr; 44(2):83-95
A lifetime of healthy skin: implications for women
WF Bergfeld

J Clin Aesthet. Dermatology 2015 Oct;8(10):21-6.
The tolerability and efficacy of a three-product anti-aging treatment regimen in subjects with moderate-to-severe photodamage
BE Katz, J Lewis, L McHugh, A Pellegrino, L Popescu

Ann Chir Plast Esthet. (translation from French) 2017 Oct;62(5):520-531.
Chemical peels and management of skin aging
Various eds.

Nurs. Women’s Health, 2017 Dec 2016 - Jan; 20(6):609-613
Skin Care for Women
AL Hodges, DK Walker

Journal Eur Acad. Dermatology Venereol. 2010 Mar;24(3):281-92
Chemical peels in aesthetic dermatology: an update, 2009
TC Fischer, E Perosino, F Poli, MS Viera, B Dreno, Cosmetic Dermatology European Expert Group

Journal of Drugs and Dermatology, 2009 Sep;8(9):803-11.
Clinical role and application of superficial chemical peels in today's practice
DS Berson, JL Cohen, MI Rendon, WE Roberts, I Starker, B Wang