Chemical Exfoliation 101: An Explanation of AHA, BHA, and PHA

Just walk into any pharmacy or the beauty section of a department store, and you’ll be confronted by an overwhelming variety of serums, moisturizers, and treatment products. Among them, AHA stands out as one of the most extensively researched and clinically proven ingredients in modern dermatology. This guide helps you cut through the marketing hype and understand exactly what chemical exfoliants can – and cannot – do for your skin.

What Are Chemical Exfoliants?

Chemical exfoliants — primarily alpha-hydroxy acids (AHAs), beta-hydroxy acids (BHAs), and polyhydroxy acids (PHAs) — are bioactive compounds that dissolve the bonds between dead skin cells, enabling them to shed more effectively. Unlike physical scrubs, these acids act at the molecular level, providing a consistent and controlled exfoliating effect without causing micro-tears that can be associated with abrasive substances. The mechanisms by which they work have been extensively studied in peer-reviewed literature, and it has been established that they are safe when used at cosmetic concentrations, making them suitable for most skin types, including sensitive and reactive skin.

The Science Behind Chemical Exfoliation

At the cellular level, AHAs, BHAs, and PHAs exert their effects by interacting with key receptors and enzyme pathways within keratinocytes—the primary surface cells of the skin. These compounds regulate gene expression related to BHA activity, enhance the skin’s natural antioxidant defenses, and support the structural proteins (such as collagen and elastin) that are essential for maintaining firmness and elasticity. Randomized controlled trials have demonstrated statistically significant improvements in the appearance of fine lines, uneven skin tone, and the integrity of the skin’s barrier function after 8–12 weeks of consistent use.

AHA: Alpha-Hydroxy Acids

AHAs are water-soluble acids that are primarily derived from fruits, milk, and sugar cane. Glycolic acid (derived from sugar cane) and lactic acid (derived from milk) are the most extensively studied and commonly used types of AHA. Due to their water-solubility, AHAs act mainly on the surface of the skin, making them particularly effective in addressing issues such as photoaging, fine lines, uneven pigmentation, and dullness. The clinical concentration of AHAs in professional exfoliating treatments ranges from 20% to 70%, while over-the-counter products usually contain 5–15% of these acids.

BHA: Beta-Hydroxy Acids

Salicylic acid is undoubtedly the most prominent BHA compound in dermatology. Unlike alpha-hydroxy acids, salicylic acid is oil-soluble, which allows it to penetrate deeply into the pores and dissolve sebum plugs. This property makes it the ideal exfoliant for people with oily, acne-prone, or combination skin types. Additionally, salicylic acid possesses inherent anti-inflammatory properties, helping to reduce the redness and swelling associated with active acne outbreaks. Concentrations of 0.5–2% are effective when used in leave-on products, while higher concentrations are typically employed in professional treatments.

PHA: Polyhydroxy Acids

PHAs — including gluconolactone, lactobionic acid, and maltobionic acid — represent the latest generation of chemical exfoliants. Due to their larger molecular size, they penetrate the skin more slowly, resulting in a milder exfoliating effect and significantly reduced irritation. PHAs are often recommended for sensitive skin, skin prone to rosacea, or those affected by eczema. In addition to their exfoliating properties, PHAs also possess humectant effects, actively drawing moisture into the skin. Moreover, they act as antioxidants, providing some protection against environmental stressors.

AHA vs BHA vs PHA: Which One Should You Choose?

Key Proven Benefits

• Reduces fine lines and wrinkles — Increases the density of dermal collagen within 8 to 16 weeks.
• Improves skin tone — Inhibits the transfer of melanin, thereby reducing the appearance of dark spots and PHA-related hyperpigmentation.
• Enhances the barrier function of the skin — Increases the production of ceramides and natural moisturizing factors.
• Unblocks pores – BHA compounds dissolve sebum blockages and help reduce the appearance of blackheads.
• Broad compatibility — When used correctly, it can be combined with most active ingredients.

How to Incorporate Chemical Exfoliants into Your Skincare Routine

For optimal results, apply chemical exfoliants to clean, dry skin as part of your evening skincare routine. Most dermatologists recommend starting with 2–3 applications per week and gradually increasing the frequency as your skin develops tolerance. Concentrations ranging from 5% to 10% AHA or 1–2% BHA are effective for most people; higher concentrations may be suitable for specific skin issues, but always under the guidance of a dermatologist. Be sure to apply a moisturizer afterwards to restore hydration, and—most importantly—apply broad-spectrum SPF 30 or higher every morning, since chemical exfoliants can significantly increase sensitivity to sunlight.

Choosing the Right Product for You

Not all chemical exfoliant formulas are created equally. Look for products that list active acids at the beginning of the INCI list, use formulations with appropriate pH levels (AHAs work best at pH 3–4; BHA at pH 3–4; PHAs at up to pH 5), and choose products with airtight or opaque packaging to maintain stability. Serum and toner forms are particularly effective for delivering exfoliants. If you are new to chemical exfoliation, start by using a PHA or a low-concentration lactic acid to assess your skin’s tolerance before moving on to glycolic acid or salicylic acid.

Possible Side Effects and Precautions

Chemical exfoliants are generally well-tolerated by most users, but some individuals may experience mild irritation, stinging, redness, or initial skin reactions—especially when used at higher concentrations or in combination with other active ingredients such as retinoids or vitamin C. To minimize these risks, it is recommended to introduce a new active ingredient one at a time, conduct a patch test on the inner forearm for 48 hours before applying it to the entire face, avoid using multiple acidic agents simultaneously, and never apply them to damaged or irritated skin. If persistent irritation occurs, reduce the frequency or concentration of use and consult a dermatologist.

Professional vs Home-Based Exfoliation

In-clinic chemical peels utilize significantly higher concentrations of acid (20–70%) under controlled conditions, enabling more noticeable results in fewer treatment sessions. Professional peels are classified into three types: superficial (affecting only the epidermis), medium-depth (reaching the papillary dermis), and deep (affecting the reticular dermis). Home-use exfoliants, on the other hand, provide gradual, cumulative benefits with minimal downtime, making them ideal for use between professional treatments. These two approaches complement each other rather than competing with one another.

Tips from Dermatologists for Maximum Effectiveness

Board-certified dermatologists recommend the following guidelines to maximize the benefits of chemical exfoliation: (1) Consistency over intensity – regular use of low-concentration products yields better results than occasional applications of high-dose formulas. (2) Patience – visible improvements usually take at least 8 weeks. (3) Avoid over-exfoliation – more is not always better; damaged skin can become sensitive, prone to breakouts, and age more rapidly. (4) Store products in a cool, dark place to maintain their effectiveness. (5) For persistent pigmentation or deep acne scars, consider combining chemical exfoliation with in-office peels or laser treatments for enhanced results.

Frequently Asked Questions

Q: Can I use AHA and BHA together?
A: Yes,
but apply them separately at first. Once your skin has gotten used to each of them, you can switch their application frequencies every other day or use a combined AHA/BHA product. Applying both at the same time on new or unexposed skin may cause irritation.

Q: When will I start to see resul
ts?
A: Initial improvements in texture and brightness can be expected within 2–4 weeks, while more significant changes in skin tone, pore size, and fine lines will become apparent after 8–12 weeks of continuous use.

Q: Is chemical exfoliation safe during pregnancy?
A: L
actic acid and PHAs are generally considered safer options during pregnancy; glycolic acid is also commonly used by many professionals. High-concentration salicylic acid should usually be avoided. Always consult your obstetrician-gynecologist or dermatologist before making any changes to your skincare routine during pregnancy or breastfeeding.

Q: Can I use exfoliants if I have active acne?
A: Low
-concentration BHA (1–2% salicylic acid) can actually help reduce active acne by unclogging pores. However, avoid using physical exfoliants on areas with active acne, and refrain from exfoliating altogether if your skin is severely inflamed or damaged.

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Please consult a licensed dermatologist before making any changes to your skincare routine.