Facial acids have become one of the most transformative categories in modern skincare. These active ingredients work by chemically exfoliating the skin — accelerating cell turnover, clearing congested pores, and improving surface texture — producing results that mechanical scrubs and basic moisturisers simply cannot match. But with so many types available, at varying concentrations and for different skin concerns, knowing where to start matters. This guide breaks down every major facial acid, explains how to choose the right one for your skin type, and shows you how to introduce them safely into your routine.
How Do Facial Acids Work?
Facial acids exfoliate the skin through a process called chemical exfoliation: they dissolve the bonds that hold dead skin cells together on the surface (or within the pores), allowing those cells to shed more efficiently. This accelerates the skin's natural renewal cycle — typically around 28 days in young adults, slowing considerably with age — revealing fresher, smoother skin beneath.
Regular use of appropriate acids can reduce the appearance of uneven pigmentation, minimise fine lines and rough texture, unclog pores, and improve the overall luminosity of the complexion. A secondary benefit is enhanced absorption: properly exfoliated skin takes up active ingredients — serums, moisturisers, and treatments — more effectively than skin with a build-up of dead cells on the surface.
Types of Facial Acids: A Complete Overview
AHA — Alpha Hydroxy Acids
AHAs are water-soluble acids that work primarily on the skin's surface. They are derived from natural sources — fruit, sugar cane, milk — and are best suited to normal, dry, and mature skin types.
- Glycolic acid — derived from sugar cane, glycolic acid has the smallest molecular weight of all AHAs, which allows it to penetrate most deeply and deliver the most noticeable results. It is effective for smoothing texture, reducing fine lines, and brightening hyperpigmentation. Its potency also means it carries the highest irritation potential of the AHA group, making gradual introduction important.
- Lactic acid — gentler than glycolic acid and derived from milk, lactic acid exfoliates while also functioning as a humectant — attracting moisture to the skin. It is well tolerated by dry and sensitive skin types and is a strong starting point for AHA beginners.
- Mandelic acid — derived from bitter almonds, mandelic acid has a larger molecule than glycolic or lactic acid, meaning slower penetration and less risk of irritation. It is particularly suited to those prone to sensitivity or post-inflammatory hyperpigmentation.
- Other AHAs — malic acid (from apples), citric acid, and tartaric acid are also classified as AHAs and appear in formulations, often in combination with glycolic or lactic acid.
BHA — Beta Hydroxy Acids
BHAs are oil-soluble, which gives them a critical advantage over AHAs: they can penetrate into the sebaceous follicle (the pore itself), dissolving excess sebum and cellular debris from within. This makes them the acid of choice for oily, acne-prone, and congestion-prone skin.
- Salicylic acid — the primary BHA used in skincare, salicylic acid is also anti-inflammatory, making it particularly effective for active breakouts rather than just prevention. It is widely used in concentrations of 0.5–2% for face products. Higher concentrations (up to 30%) are used in professional clinical peels. Those with aspirin sensitivity should use salicylic acid products with caution.
PHA — Polyhydroxy Acids
PHAs are the newest generation of exfoliating acids and are distinguished by their large molecular size. They exfoliate more slowly and cannot penetrate as deeply as AHAs or BHAs, which makes them significantly less likely to cause irritation or sensitisation. PHAs are the appropriate starting point for anyone with genuinely sensitive, reactive, or rosacea-prone skin.
- Gluconolactone — the most common PHA in skincare, gluconolactone exfoliates gently while also providing antioxidant protection and moisture retention.
- Lactobionic acid — a PHA derived from milk sugar (lactose), with particularly strong hydrating and antioxidant properties alongside its gentle exfoliation.
- Glucoheptonolactone — similar profile to gluconolactone; mild exfoliation with barrier-supportive properties.
Hyaluronic Acid
Despite its name, hyaluronic acid is not an exfoliating acid — it is a humectant, meaning it draws water from the environment and deeper skin layers to the surface, maintaining skin hydration and plumpness. It occurs naturally in the body and is exceptionally well tolerated. In skincare, it appears across a range of molecular weights: high molecular weight HA sits on the surface and provides immediate plumping; low molecular weight HA penetrates more deeply for longer-lasting moisture effects.
Azelaic Acid
Azelaic acid occupies a unique position in skincare: it is not purely an exfoliating acid but a multifunctional active with antibacterial, anti-inflammatory, and brightening properties. It inhibits the enzyme tyrosinase (involved in melanin production), making it effective for hyperpigmentation and post-acne marks. At the same time, its anti-inflammatory action makes it useful for rosacea and sensitive skin — a rare combination. Azelaic acid is used at concentrations of 5–10% in over-the-counter products and up to 20% in prescription formulas.
Ferulic Acid
Ferulic acid is primarily an antioxidant rather than an exfoliant. It is most commonly used in formulations alongside vitamin C and vitamin E, where it both enhances and stabilises the activity of those antioxidants. It helps protect skin from UV-induced free radical damage and is a staple ingredient in anti-ageing serums.
[products:the-ordinary-glycolic-acid-7-exfoliating-toner-240-ml, isntree-chestnut-aha-8-clear-100-ml, cosrx-aha-bha-clarifying-treatment-toner-150-ml, isntree-chestnut-bha-0-9-clear-toner-200-ml, cos-de-baha-s4-salicylic-acid-bha-4-serum-30-ml, cos-de-baha-az-azelaic-acid-10-serum-30-ml, some-by-mi-aha-bha-pha-30-days-miracle-serum-50-ml, the-ordinary-mandelic-acid-10-ha-30-ml]How to Choose the Right Facial Acid for Your Skin Type
Dry and Sensitive Skin
Prioritise lactic acid (AHA) for gentle exfoliation combined with moisture retention, or a PHA such as gluconolactone if even lactic acid proves too stimulating. Hyaluronic acid is essential in any dry-skin routine — use it regardless of whichever exfoliating acid you choose. Azelaic acid is also well tolerated and brings brightening benefits without the stripping effect of higher-potency AHAs.
Oily and Acne-Prone Skin
Salicylic acid (BHA) is the clear first choice. Its oil-soluble nature allows it to work inside the pore, dissolving the sebum and dead cell plugs that cause breakouts. Begin with a low concentration (0.5–1%) to assess tolerance before moving to 2%. Azelaic acid makes a strong companion or alternative, particularly for those experiencing post-inflammatory hyperpigmentation alongside active congestion.
Combination Skin
A targeted approach works well: apply BHA to the T-zone where oiliness and congestion are concentrated, and AHA (lactic or mandelic acid) to drier areas of the face. Multi-acid products containing both AHA and BHA at moderate concentrations are also a practical option for combination skin types.
Mature and Ageing Skin
Glycolic acid (AHA) delivers the most pronounced smoothing and resurfacing effects and is the best-supported acid for reducing fine lines and improving skin firmness over time. Ferulic acid — used in combination with vitamins C and E — adds powerful antioxidant protection against the environmental damage that accelerates ageing. Consider alternating glycolic acid exfoliation with a ferulic acid vitamin C serum for a comprehensive anti-ageing approach.
Sensitive and Reactive Skin
PHAs are the appropriate entry point. If PHA causes no reaction after several weeks, consider introducing lactic acid at a low concentration (5%). Azelaic acid is also well suited to genuinely sensitive skin. Avoid glycolic acid and high-concentration BHAs until the skin barrier is stronger. Our facial acids, oils and serums collection includes products across all sensitivity levels.
[products:cos-de-baha-h-hyaluronic-acid-serum-120-ml, isntree-hyaluronic-acid-toner-plus-200-ml, the-ordinary-hyaluronic-acid-2-b5-30-ml, the-ordinary-niacinamide-10-zinc-1-30-ml, cos-de-baha-nz-niacinamide-20-zinc-pca-4-serum-30-ml, cosrx-hyaluronic-acid-hydra-power-essence-100-ml]How to Introduce Facial Acids Safely: A Step-by-Step Approach
The most common mistake with facial acids is moving too fast. Skin needs time to adapt, and a gradual introduction dramatically reduces the risk of irritation, barrier disruption, or rebound sensitivity.
- Start with a low concentration. Begin with the lowest available percentage — for glycolic acid, this means 5–7%; for salicylic acid, 0.5–1%; for AHA/BHA combinations, look for beginner-friendly formulations.
- Use once a week initially. Apply your chosen acid on one evening per week. Observe how your skin looks and feels over the following 48 hours.
- Increase frequency gradually. If no significant redness, peeling, or irritation appears after 2–3 weeks, increase to twice weekly. Most established users settle at 2–3 times per week for maintenance.
- Cleanse first. Always apply acids to thoroughly cleansed skin, free from make-up, SPF, and other products. Residual film can interfere with even product penetration.
- Apply evenly and sparingly. A small, even application is more effective and less irritating than a heavy coat. Avoid the immediate eye area, nostrils, and lips.
- Follow with moisturiser. After the acid has absorbed (typically 10–20 minutes), apply a moisturiser or hydrating serum. Hyaluronic acid serum under moisturiser is an excellent pairing for any exfoliating acid.
- Apply SPF every morning without exception. Exfoliating acids increase the skin's sensitivity to UV radiation — the new cells revealed are more vulnerable than the old ones removed. Use broad-spectrum SPF 30 or higher every morning, including during overcast weather. Browse our sun protection collection for suitable daily SPF options.
Common Mistakes to Avoid
Understanding what not to do with facial acids is as important as knowing how to use them correctly. The most frequent errors are using acids too often before the skin has adapted; combining multiple strong actives (such as an AHA and retinol) in the same application; skipping SPF; choosing an acid that is wrong for the skin type; applying too much product; and neglecting moisturisation after exfoliation. Any sustained redness, burning sensation, or excessive peeling is a signal to reduce frequency or switch to a gentler acid. If in doubt, consult a dermatologist — particularly if you have rosacea, eczema, or other pre-existing skin conditions. For a wider selection of active skincare, explore our facial cosmetics collection.
[warning:Perform a patch test before applying any new acid product to the full face. Apply a small amount to the inner forearm and observe for 24–48 hours. People with rosacea, perioral dermatitis, eczema, or compromised skin barrier should consult a dermatologist before introducing exfoliating acids. Never use high-concentration AHA or BHA products on broken, sunburned, or recently treated skin. Always apply SPF the morning after using any exfoliating acid.] [note:All Medpak products are shipped from within the EU, ensuring fast, reliable delivery with no customs fees for customers across Europe.]
