AHA, BHA, PHA & LHA: Chemical Exfoliation Explained

Exfoliation is a great way to enhance your skincare routine, helping to remove dead skin cells and reveal a fresher, more radiant complexion. As we age, the skin’s natural renewal process slows down, leading to dullness, rough texture, and congestion. By incorporating the right exfoliant, you can promote smoother skin, refine pores, and improve the absorption of other skincare products.

In our previous guide on exfoliation, we introduced both physical and chemical methods, exploring their benefits and drawbacks. While physical exfoliants—like scrubs with rough beads—can provide quick results, they often cause micro-tears and irritation, making them less ideal for long-term skin health. That’s where chemical exfoliation stands out. When used correctly, it delivers consistent, controlled exfoliation without disrupting the skin barrier. In this guide, we’ll focus entirely on chemical exfoliation, breaking down how it works, its benefits, and how to choose the right one for your skin.

How Chemical Exfoliants Work

Chemical exfoliants work by breaking down the bonds that hold dead skin cells together, allowing them to be shed more easily. This process promotes healthy cell turnover and is generally more effective and less abrasive than physical exfoliation.

There are four main types of chemical exfoliants, each with unique properties:

Alpha Hydroxy Acids (AHAs)

AHAs are water-soluble acids that work on the skin’s surface, making them ideal for treating dullness, sun damage, and uneven texture. They are particularly beneficial for dry and sun-damaged skin, as they help retain moisture while exfoliating.

Common AHAs and Their Properties:

Glycolic Acid: Derived from sugar cane, glycolic acid has the smallest molecular size among AHAs, allowing for deeper penetration into the skin. It’s effective at improving texture, reducing fine lines, and brightening skin.

Typical concentration: 5-10% in leave-on products; up to 20% in professional treatments.

Lactic Acid: Sourced from milk, lactic acid is gentler than glycolic acid and is excellent for sensitive or dry skin.

Typical concentration: 5-10% in leave-on products.

Mandelic Acid: Derived from almonds, mandelic acid has larger molecules, making it a good option for sensitive skin and acne-prone skin.

Typical concentration: 5-10% in leave-on products.

Malic Acid: Found in apples, malic acid is often used in combination with other AHAs for enhanced exfoliation and hydration.
Tartaric Acid: Extracted from grapes, tartaric acid primarily stabilizes other AHAs and enhances their efficacy.
Citric Acid: Sourced from citrus fruits, citric acid exfoliates while providing skin-brightening benefits.

Beta Hydroxy Acids (BHAs)

BHAs are oil-soluble, meaning they can penetrate deeper into pores, making them highly effective for oily and acne-prone skin. The most common BHA is salicylic acid, known for its ability to unclog pores, reduce blackheads, and control oil production.

Salicylic Acid and Concentrations:

Leave-on products: Typically 0.5-2% for effective exfoliation.
Rinse-off products: Up to 3% (but require extended contact time for effectiveness).
At very low concentrations (0.5%), it primarily acts as a skin-soothing and anti-inflammatory ingredient rather than an exfoliant.

Polyhydroxy Acids (PHAs)

PHAs function similarly to AHAs but have larger molecules, meaning they penetrate the skin less deeply, causing less irritation. This makes them ideal for sensitive skin and conditions like rosacea or eczema.

Key PHAs:

Gluconolactone: Provides gentle exfoliation and hydration while strengthening the skin barrier.
Lactobionic Acid: A PHA with antioxidant properties that enhances moisture retention and minimizes fine lines.

Lipohydroxy Acids (LHAs)

LHAs are a derivative of salicylic acid that work more slowly, making them less irritating. They offer similar benefits to BHAs but are more suitable for sensitive and acne-prone skin.

Tips for Beginners in Chemical Exfoliation

Establish a solid skincare foundation first: Before adding exfoliation, ensure you have a proper routine with cleansing, moisturizing, and SPF.
Start Slowly: Begin with once a week and gradually increase frequency based on tolerance.
Patch Test: Always test new products on a small area to check for reactions, wait at least 24 hours, and observe for any signs of irritation before incorporating the product into your routine.
Use Sunscreen: AHAs increase sun sensitivity, making SPF 30+ an essential step in your routine. While other chemical exfoliants are generally not known to heighten photosensitivity, we still emphasize daily sunscreen use to provide extra protection and maintain healthy-looking skin.
Avoid Over-Exfoliation: Signs of over-exfoliation include prolonged redness, skin dehydration and peeling, acne flare-ups, and irritation. Take a break and let your skin recover, if these occur.
Opt for Leave-On Products (unless very sensitive) as they provide better results than rinse-off exfoliants.

Choosing the Right Exfoliant Based on Your Skin Type

Finding the right chemical exfoliant depends on your skin type, concerns, and tolerance. Below is a detailed breakdown of which exfoliants work best for different skin types and how to incorporate them into your routine.

Dry Skin: AHAs are generally the best option for dry skin since they exfoliate while also providing hydration. Lactic acid is a good starting point as it is gentler and helps maintain moisture balance. For beginners, a combination of low-concentration AHAs and BHAs can be a gentle introduction to exfoliation. Beauty of Joseon Green Plum Refreshing Toner (AHA + BHA) is a great choice, as it provides mild exfoliation while maintaining hydration and minimizing irritation.
Oily / Acne-Prone Skin: BHAs, particularly salicylic acid, are ideal for those with excess oil production and acne. They penetrate deep into the pores, unclogging them and reducing inflammation. A great option is Benton AC BHA Gel, which not only contains salicylic acid but also soothing ingredients like heartleaf, tea tree, and Centella Asiatica extracts, making it perfect for acne-prone skin without causing excessive dryness. Additionally, since it is a moisturizer, it eliminates the need for an extra step in your routine, helping to simplify skincare without overwhelming the skin.
Sensitive Skin: PHAs are the gentlest exfoliants, making them ideal for sensitive skin. Unlike AHAs and BHAs, PHAs have larger molecules, which means they work on the surface and cause less irritation. If you are just starting out, rinsing off exfoliants is a better option. The Benton PHA Peeling Gel is a great choice as it is balanced with ceramides and hyaluronic acid to maintain the skin barrier and hydration while providing mild exfoliation. If your skin is actively irritated, it’s best to skip exfoliation until it recovers.
Combination Skin: Those with combination skin can benefit from using different types of exfoliants. LHAs are a great option as they work similarly to BHAs but are gentler. A mild yet effective choice is Anua Heartleaf LHA Moisture Peeling Gel, which exfoliates while hydrating. Alternatively, a balanced AHA/BHA formula like COSRX AHA/BHA Clarifying Treatment Toner can help target both dry and oily areas effectively.

Chemical exfoliation is a fantastic addition to any skincare routine when used correctly. It helps reveal fresh, glowing skin while avoiding the harsh effects of physical scrubs. However, moderation is key—over-exfoliation can do more harm than good. If an exfoliant doesn’t work for you, don’t be discouraged. Skincare is highly individual, and finding the right fit takes time.

Start slow, choose the right exfoliant for your skin type, and always prioritize hydration and sun protection. Your skin will thank you for it!

References:

Harvard Health Publishing, Have you exfoliated lately?

American Academy of Dermatology Association, How to safely exfoliate at home

Dermascope, Alpha, Beta, Enzymes: The Science of Chemical Exfoliation

Experimental Dermatology, July 2019, pages 786-794

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