At its core, a chemical peel accelerates desquamation, the skin’s natural shedding process, by dissolving the intercellular "glue" (desmosomes) that binds dead corneocytes together. This reveals the fresher skin underneath and can even stimulate collagen production over time [1]. Understanding the fundamental differences between acid families is the first step to choosing correctly.

• Alpha-Hydroxy Acids (AHAs): Water-soluble surface resurfacers like Glycolic and Lactic Acid. Best for normal-to-dry, sun-damaged skin concerned with dullness, uneven texture, and fine lines [2].
• Beta-Hydroxy Acid (BHA): Oil-soluble Salicylic Acid. Its unique ability to penetrate sebum makes it the gold standard for clearing congested pores and managing acne in oily and combination skin types [3].
• Poly-Hydroxy Acids (PHAs): The gentle giants like Gluconolactone and Lactobionic Acid. Their large molecular size ensures slow, superficial penetration, making them ideal for sensitive or rosacea-prone skin [4].
• Lipo-Hydroxy Acid (LHA): A newer, highly lipophilic derivative of salicylic acid. Its very slow, cell-by-cell exfoliation offers BHA-like benefits with an even lower risk of irritation, making it exceptionally well-suited for sensitive, acne-prone skin [5].

A common misconception is that a higher percentage is always stronger. The real potency of a peel is a function of its concentration, its pH, and the acid's inherent strength (pKa value). For consumer safety, regulatory bodies have established clear guidelines for products intended for home use.

Typically, at-home AHA products are formulated at concentrations of 10% or less, with a final pH no lower than 3.5. For BHA, the leave-on limit is generally 2% [1, 6]. The reason for this pH floor is critical: the lower a product's pH falls below the acid's pKa, the more "free acid" is available to work on the skin, making it exponentially more aggressive.

In stark contrast, professional-grade peels operate in a territory that is unsafe for home use. These may include:

• Glycolic acid at concentrations of 30-70%.
• Trichloroacetic acid (TCA) peels, which are strictly medical procedures.
• Combination peels like the Jessner’s solution.

These professional formulations often have a very low pH (sometimes below 2.0), designed to induce a much deeper and more controlled injury to the skin. They require the expertise of a dermatologist or licensed aesthetician to manage application, timing, and potential side effects like burns, scarring, and severe post-inflammatory hyperpigmentation.

The term "acid" in skincare is often mistakenly equated with exfoliation. Many acids serve entirely different, vital functions.

• Hyaluronic Acid: Is a polysaccharide (a sugar), not an exfoliant. It is a powerful humectant that draws moisture into the skin.
• L-Ascorbic Acid (Vitamin C): Primarily functions as a potent antioxidant, neutralising free radical damage. While very high concentrations at a very low pH can exhibit some exfoliating properties, this is a secondary effect, not its main purpose.
• Ferulic Acid: Another powerful antioxidant, often paired with Vitamins C and E to enhance their stability and photoprotective benefits. It does not exfoliate.
• Tranexamic Acid: Works by inhibiting pigment pathways (tyrosinase and plasmin) in the skin. It is highly effective for treating hyperpigmentation, such as melasma and post-inflammatory marks, but it does so without exfoliating.

1. Select by Skin Type and Start Slow: Begin with a low-concentration product once or twice a week to assess your skin's tolerance. There is no prize for rushing.
2. Be Mindful of Other Potent Actives: The most critical rule is to avoid using chemical exfoliants on the same night as retinoids (retinol, tretinoin). Both are powerful resurfacing agents, and using them together is a fast track to severe irritation and a compromised barrier. Alternate nights for each active to allow your skin time to recover.
3. Support Your Skin Barrier: Chemical exfoliation is a controlled injury. Follow up on peel nights (and every other night) with barrier-fortifying ingredients like ceramides, panthenol, cholesterol, and niacinamide to hydrate, soothe, and rebuild.
4. Sunscreen is Non-Negotiable: Exfoliated skin is more vulnerable to UV radiation [1]. Daily use of a high-SPF (30 or higher), broad-spectrum sunscreen is absolutely critical to protect your fresh skin, prevent rebound hyperpigmentation, and see the true benefits of your efforts.

Effective chemical exfoliation is a science, not a numbers game. A successful outcome depends on a sophisticated understanding of not just the acid type and concentration, but also the product's pH, your skin's tolerance, and the other actives in your routine. By selecting an exfoliant tailored to your skin's unique needs and prioritising a "less is more" approach, barrier support, and diligent sun protection, you can safely leverage the transformative power of these ingredients for healthier, more radiant skin.