Skin Care Education

AHA (Alpha Hydroxy Acids)

A family of water-soluble exfoliating acids that work at the skin surface to dissolve the bonds holding dead cells together, improving texture, brightness, and tone.

What Are Alpha Hydroxy Acids?

Alpha hydroxy acids, commonly abbreviated to AHAs, are a family of naturally occurring organic acids widely used in both professional aesthetic treatments and consumer skincare. They are water-soluble, meaning they work primarily at the surface of the skin rather than penetrating into the pore. Their primary mechanism of action is chemical exfoliation: AHAs weaken the bonds between dead skin cells in the outermost layer of the epidermis, facilitating their removal and accelerating the skin’s natural cell turnover process.

The most commonly used AHAs in aesthetic practice include glycolic acid, derived from sugarcane and the smallest molecule in the family, giving it the deepest penetration of the group; lactic acid, derived from milk and fermented sugars, with a larger molecule size that makes it gentler and better tolerated by more sensitive skin types; mandelic acid, derived from bitter almonds, with the largest molecule and the mildest action; malic acid, from apples; and citric acid, from citrus fruits. Each has a slightly different profile of activity, tolerability, and clinical application.

AHAs are used across a wide range of professional treatments and skincare formulations, from leave-on serums and toners at low concentrations to professional chemical peels at higher concentrations. Their ability to improve skin texture, reduce the appearance of fine lines and uneven pigmentation, and enhance the penetration of other active ingredients makes them one of the most versatile and evidence-supported categories in aesthetic skincare.

What to Expect

The experience of AHA-based treatments varies considerably depending on the concentration, the specific acid used, the application method, and the individual skin type.

At the lower concentrations found in leave-on skincare products, typically between 5 and 10 percent, the sensation is usually mild and may include a brief tingling or warmth on application. Regular use at these concentrations produces gradual improvements in skin texture, brightness, and tone over several weeks.

Professional AHA peels are applied at higher concentrations, typically between 20 and 70 percent, and produce a more pronounced exfoliating response. During a professional peel, a tingling or stinging sensation is normal and expected. The strength and duration of the sensation depends on the concentration and the contact time. Most peels are neutralised after a controlled period and the sensation resolves quickly. Some redness and mild flaking in the days following a professional peel is normal and reflects the exfoliation process. Downtime is typically minimal for superficial peels and more significant for medium-depth applications.

Results from AHA treatments build over time with consistent use. A single professional peel will produce a visible improvement in skin brightness and texture. A course of treatments produces more significant and lasting improvement in tone, pigmentation, and surface quality.

Who It’s For and Results

AHAs are suitable for a broad range of skin types and concerns, making them one of the most widely applicable categories of exfoliating active. They are particularly well suited to individuals looking to improve overall skin texture and radiance, those with dull or uneven complexions from accumulated dead skin cell build-up, and those with mild to moderate sun damage, uneven pigmentation, or post-inflammatory marks.

Lactic and mandelic acids are the preferred options for those with more sensitive skin, darker skin tones, or those new to chemical exfoliation, as their larger molecular size produces a gentler and more controlled exfoliating response with a lower risk of irritation. Glycolic acid, with its smaller molecule and deeper penetration, is well suited to those with normal to resilient skin seeking more significant textural improvement and collagen-stimulating effects.

AHAs are not recommended for use on actively inflamed or broken skin, and their use requires consistent sun protection, as exfoliation increases the skin’s sensitivity to UV radiation. They are generally well tolerated but can cause irritation, redness, and increased sensitivity if overused or used at too high a concentration for the individual skin type.

With consistent professional treatment and appropriate homecare, AHAs deliver reliable improvements in skin texture, tone evenness, brightness, and the appearance of fine lines. They also support the effectiveness of other active ingredients by clearing the dead cell layer that can impede their penetration.

Frequently Asked Questions: Alpha Hydroxy Acids

Both AHAs and BHAs are chemical exfoliants, but they differ in their solubility and where they work in the skin. AHAs are water-soluble and work primarily at the skin surface, making them effective for improving overall texture, tone, and brightness. BHAs, primarily salicylic acid, are oil-soluble and can penetrate into the pore lining alongside sebum, making them particularly effective for treating congestion, blackheads, and acne-prone skin. AHAs are generally better suited to dry, sun-damaged, or dull skin focused on surface improvement. BHAs are generally better suited to oily, congested, or acne-prone skin.

The appropriate frequency depends on the concentration, the specific AHA, and the individual skin type. Leave-on products at lower concentrations can typically be used daily or every other day once the skin has adjusted. Professional peels are generally applied in a course of four to six sessions spaced two to four weeks apart, with maintenance treatments thereafter. Beginning with lower concentrations and less frequent use and gradually increasing as the skin tolerates is the standard approach for introducing AHAs, whether in professional or homecare contexts.

Yes. By removing the outermost layer of dead skin cells, AHAs temporarily increase the skin’s sensitivity to ultraviolet radiation. This makes consistent daily use of broad-spectrum SPF essential when using any AHA-containing product or undergoing AHA-based professional treatments. Failing to protect the skin from UV during and after AHA use can lead to increased pigmentation, undoing the brightening effects the treatment was intended to produce.

Yes, but the choice of AHA and concentration requires consideration of skin tone. Darker skin tones have a higher melanocyte density and are more prone to post-inflammatory hyperpigmentation in response to irritation or inflammation. For this reason, gentler AHAs such as lactic or mandelic acid, at appropriate concentrations and with careful introduction, are generally preferred for medium to deeper skin tones. With appropriate selection and protocol, AHAs can be safely and effectively used across the full spectrum of skin tones.