Acids might initially sound intimidating, especially if you have sensitive skin, but, when formulated correctly, work gently to target dark spots, hyperpigmentation, fine lines and more. Read on, to learn all about acids and find the right ones for your skin type and concerns. Here is our complete guide to acids!
Acids should be a staple in everyone’s skincare regimen. They vary in structure, size, and chemical properties and therefore vary in function and skin benefits. We will break down our favorite acids by structure, exploring how it dictates the function and therapeutic use, enabling anyone to pick the acids best suited to their skin concern.
Skincare acids go beyond just exfoliation. Each acid has additional benefits such as antibacterial, antiglycation, comedolytic, and anti-inflammatory properties. Acids also help lower the pH of your skin, which is naturally acidic. Studies have also shown that lowering the pH of your stratum corneum enhances bioprocesses and can help with your skin’s innate immunity and microbiome. Acidic pH treatments, such as the use of topical acids, enhance barrier recovery, improve stratum corneum cohesion, and improve skin hydration.1
Alpha Hydroxy Acids
Alpha hydroxy acids have a hydroxyl or OH group on the alpha or adjacent carbon of the carboxyl group. These acids are keratolytic agents, softening and loosening the upper layers of the stratum corneum to promote shedding. AHAs work to reveal smoother, brighter, and more youthful skin. The common AHAs include glycolic acid, lactic acid, mandelic acid, tartaric acid, and malic acid.
Glycolic acid is the smallest of the alpha hydroxy acids, weighing in around 76 Daltons. Due to its small molecular weight, it works on both the epidermal and dermal layers, increasing collagen and hyaluronic acid synthesis in the skin.2 It also regulates matrix degradation seen in photoaging and increases epidermal thickness. It has antibacterial properties when formulated below pH 4.00 and brightens skin by not only increasing cell turnover, but also by acting as a tyrosinase inhibitor.3,4 Glycolic Acid restores skin elasticity and vitality, fades spots and imperfections, evens skin texture and tone, enhances skin radiance, and improves fine lines and wrinkles.
Mandelic acid is an aromatic alpha hydroxy acid, making it more lipophilic or oil soluble than other AHAs, meaning it penetrates pores easier. On the other hand, it has a molecular weight, twice that of glycolic acid (152 Daltons), so it penetrates the skin more slowly. One study shows that mandelic acid increases sebum production, making it great for those with dry skin.5 The mechanisms of this acid are not all known, but it is known that it strengthens and supports collagen production, inhibits tyrosinase, and has antibacterial and anti-inflammatory properties. Mandelic Acid reduces blemishes and congestion, especially inflammatory congestion, while addressing discoloration, fine lines and wrinkles, and skin elasticity.
Beta Hydroxy Acids
Beta hydroxy acids have a hydroxyl or OH group on the beta carbon or two carbons down from the carboxyl group. Although citric acid can be seen as both an alpha hydroxy acid and a beta hydroxy acid, salicylic acid is the only skincare acid, commonly referred to as a beta hydroxy acid. This beta hydroxy acid shares similar benefits with alpha hydroxy acids, including exfoliation, reduction in hyperpigmentation, and evening of skin texture.
Salicylic Acid, like mandelic acid, has an aromatic benzene ring, but is less water soluble than mandelic acid. The hydrophobicity allows salicylic acid to work inside the pores, clearing excess sebum and debris, resulting in reduced skin congestion and potentially pore size. It also means that salicylic acid’s exfoliation is not as pH dependent as the alpha hydroxy acids. This benzene ring also helps salicylic acid inhibit UVB-induced sunburn cell formation, so as to not increase skin UV-sensitivity, as seen with alpha hydroxy acids.6 It acts as a comedolytic, desmolytic, and anti-inflammatory agent. For a deeper dive on salicylic acid, read our article Everything You Need to Know About Our BHA Exfoliating Liquid 2%.
The prefix “poly” means “many,” thus polyhydroxy acids have two or more hydroxyl or OH groups on the molecule. The polyhydroxy acids are seen as “second generation” AHAs, since one of the hydroxyl groups is on the alpha carbon, therefore giving PHAs similar skin benefits as AHAs, but with some additional advantages.7 PHAs are larger molecules than AHAs, so their penetration is limited and gradual, which means less irritation for those with sensitive skin.8 The multiple hydroxyl groups also attract water, providing additional moisturization. Their antioxidant properties help prevent oxidative damage from UV exposure and fight glycation, sugar-induced sallowness and skin sagging. PHAs enhance skin barrier function and can enhance the therapeutic benefits of other actives.9
Azelaic Acid is a dicarboxylic acid, meaning there are two carboxyl functional groups on the molecule, one on each side of the carbon chain. It does not have hydroxyl or OH groups along the carbon chain, like AHAs or BHA. Azelaic acid is a “skin balancing” ingredient, addressing bioprocesses in the skin that are overreacting, and bringing them back to a normal state. This skin normalizer decreases hyperpigmentation without impacting normal pigmentation, normalizes cell turnover, and reduces blemishes without reducing sebum production. Due to its high molecular weight, it is a more gentle exfoliant and actually reduces skin sensitivity by reducing proinflammatory agents and acting as an antioxidant. Azelaic acid provides comedolytic and antimicrobial benefits to address blemishes while minimizing impact on skin’s natural microflora.10 It is commonly used to treat both acne and rosacea.10 We chose to use an advanced azelaic acid derivative in our formula, potassium azeloyl diglycinate, which combines the benefits of azelaic acid and glycine, in addition to normalizing sebum production. Azelaic acid reduces bumps and evens skin texture, improves hyperpigmentation, reduces redness and inflammation, fades post-acne marks, and both treats and prevents skin congestion.
Tranexamic acid is a monocarboxylic acid, structurally similar to the amino acid lysine. Tranexamic acid originates from the medical field and is used orally to reduce excessive bleeding. Topically, it is a potent skin brightener, normalizing pigment abnormalities such as melasma, post inflammatory hyperpigmentation, UV induced discoloration, and acne scarring. Tranexamic acid acts as both a competitive tyrosinase inhibitor, as well as a plasmin inhibitor, addressing two different mechanisms in melanogenesis or pigment production.11 Naturium’s Tranexamic Acid 5% also contains kojic acid. Kojic acid is a pyrone, known for chelating or binding metals, and does not fall into the carboxylic acid family.Kojic acid acts as a tyrosinase inhibitor by chelating copper ions essential to melanogenesis. Naturium’s combination of tranexamic acid and kojic acid target multiple mechanisms of pigment production, to treat the most stubborn discoloration and uneven skin tone.
Acids can easily be incorporated into any skincare regimen. They work on all skin types, for a multitude of benefits.