What’s the Difference Between AHAs and BHAs?

In the realm of modern skincare, acids are no longer reserved for intimidating chemical peels or niche dermatological treatments. Alpha hydroxy acids (AHAs) and beta hydroxy acids (BHAs) have earned their place on the shelves of mainstream beauty enthusiasts and professionals alike. But while both offer remarkable exfoliating benefits, their distinct properties mean they behave quite differently on the skin.

This article offers a clinical, evidence based exploration of AHAs and BHAs: their origins, how they function at the cellular level, and who should be using them or avoiding them in their skincare regime.

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Understanding Exfoliation: Why Acids Matter

Before delving into the specifics of AHAs and BHAs, it is helpful to understand why exfoliation is so vital. Our skin undergoes a continuous process of renewal, shedding dead skin cells from the stratum corneum to reveal fresher, more vibrant skin underneath. However, this process can slow with age, environmental stressors, or certain skin conditions.

Chemical exfoliants such as AHAs and BHAs dissolve the bonds between dead skin cells, aiding their removal without the mechanical abrasion associated with scrubs. When used correctly, they promote smoother texture, improved tone, and enhanced product absorption.

What Are AHAs?

Alpha hydroxy acids (AHAs) are a group of naturally occurring acids most often derived from sugary fruits, milk, or plants. Common types include:

• Glycolic acid (from sugar cane)

• Lactic acid (from sour milk)

• Citric acid (from citrus fruits)

• Mandelic acid (from bitter almonds)

• Tartaric acid (from grapes)

AHAs are water soluble, which means they work predominantly on the surface layers of the skin. Their primary function is to loosen the cohesive 'glue' between dead skin cells, allowing them to slough off more easily. AHAs are renowned for improving skin tone, reducing hyperpigmentation, smoothing fine lines, and promoting collagen production.

Key Benefits of AHAs:

• Enhanced skin radiance

• Increased hydration (particularly lactic acid, which is a humectant)

• Reduction in visible signs of sun damage

• Smoother, more even skin texture

Ideal For:

Dry, dull, or ageing skin types seeking surface exfoliation and hydration.

What Are BHAs?

Beta hydroxy acids (BHAs) are oil soluble, allowing them to penetrate the skin’s sebum filled pores more deeply. The most common and widely studied BHA is salicylic acid, a derivative of willow bark, wintergreen leaves, or sweet birch.

Because BHAs can penetrate through oil, they are especially effective at exfoliating within the pores, dissolving excess sebum, and helping to prevent comedones (blackheads and whiteheads). BHAs also exhibit anti inflammatory and antibacterial properties, making them beneficial for acne prone skin.

Key Benefits of BHAs:

• Deep pore cleansing

• Reduced breakouts and blackheads

• Calming of inflammation and redness

• Regulation of oil production

Ideal For:

Oily, congested, acne prone, or combination skin types.

AHAs vs BHAs: A Comparative Look

Property	AHAs	BHAs
Solubility	Water soluble	Oil soluble
Skin Penetration Level	Surface only	Deeper into pores
Primary Use	Brightening, smoothing, hydrating	Unclogging pores, anti acne
Skin Type Suitability	Dry, dull, sun damaged	Oily, acne prone, sensitive
Notable Examples	Glycolic, Lactic, Mandelic	Salicylic acid
Side Notes	May cause stinging or irritation	More gentle in lower concentrations

Are They Safe to Use Together?

In many formulations, AHAs and BHAs are combined to offer dual action exfoliation surface refinement from AHAs and pore cleansing from BHAs. However, this requires careful formulation and application. Overuse or layering multiple acid based products can lead to barrier disruption, irritation, or increased photosensitivity.

If introducing both to a skincare routine:

• Start with lower concentrations

• Use on alternate days

• Always follow with broad spectrum SPF, as both increase UV sensitivity

Choosing the Right Acid for Your Skin

1. Dry or Mature Skin: Opt for AHAs, particularly lactic acid or mandelic acid, which are gentler and hydrating.

2. Oily or Acne Prone Skin: BHAs like salicylic acid are more effective due to their ability to enter and clear out oily pores.

3. Sensitive Skin: Start with a low concentration (under 5%) of either acid type. Mandelic acid (AHA) and low dose salicylic acid (BHA) are generally well tolerated.

4. Uneven Tone or Pigmentation: AHAs, especially glycolic acid, are helpful in fading hyperpigmentation with regular use.

Clinical Caution: When to Avoid Acids

• Compromised skin barriers (eczema, rosacea flare ups, severe sensitivity) may react negatively to acids.

• Pregnant or breastfeeding women should consult a medical professional before using BHAs, as high concentrations of salicylic acid are under clinical scrutiny.

• Avoid combining acids with retinoids or vitamin C unless under dermatological supervision.

Final Thoughts from Dr Claudia Moreau

Alpha hydroxy acids and betahydroxy acids represent two sides of the exfoliation spectrum both elegant in their function, yet uniquely suited to different skin challenges.

Their increasing popularity is no accident: when used responsibly and with scientific understanding, they can dramatically improve the health and appearance of the skin.

Ultimately, informed skincare is effective skincare. As always, consult a qualified aesthetician or dermatologist when introducing new active ingredients into your routine, especially those as potent as AHAs and BHAs.