Using acids correctly: AHA, BHA and PHA explained

Acids are among the most effective ingredients in modern skincare. Used correctly, they can restore radiance to dull skin, unclog pores, and smooth fine lines. But as beneficial as their benefits are, if used incorrectly, they can quickly lead to irritation. In this article, you'll learn how the three most important acids in skincare—AHA, BHA, and PHA—work, how they differ, and how to safely incorporate them into your routine step by step.

What are AHA, BHA and PHA?

Behind the abbreviations lie three different groups of exfoliants, each of which has its own way of removing dead skin cells and stimulating cell renewal.

AHA (alpha hydroxy acids) such as glycolic acid or lactic acid are water-soluble acids that dissolve dead cells on the skin's surface, thus creating a smoother complexion. They can improve skin texture, reduce slight pigmentation (e.g., caused by sun damage or acne scars), and make the skin appear fresher. Studies also show a supportive effect on moisture retention and a slight improvement in fine lines – although without lasting "wrinkle elimination."

BHA (beta-hydroxy acid) – in skin care almost always salicylic acid – can penetrate into the pores, where it dissolves dead cells and sebum residue. This cleanses pores and makes the skin appear clearer. Salicylic acid also has anti-inflammatory properties, which can be helpful for inflammatory pimples. However, it doesn't have a true antibacterial effect like benzoyl peroxide.

PHA (polyhydroxy acids) such as gluconolactone or lactobionic acid (Sugar acid) have a similar effect to AHAs, but have larger molecules. They penetrate the skin more slowly and are therefore considered milder. PHAs gently exfoliate dead skin cells and have antioxidant and moisturizing effects. Despite their better tolerability, they can also cause irritation in higher concentrations.

Which acid is suitable for whom?

The key to success is choosing the acid that suits your skin type and goals.

AHAs are useful for skin that appears dull, prone to dryness, or suffers from pigmentation irregularities. They are often used for photodamaged skin and can be beneficial for more mature skin types due to their improved texture. Lactic acid is considered a milder alternative, while glycolic acid is more potent but can also be more irritating.

BHA is particularly suitable for oily skin, clogged pores, blackheads, and acne. It's also a good choice for combination skin, as it effectively combats impurities in oily areas. But be careful: every combination skin reacts differently – some tolerate BHA all over the face, others only in the T-zone or at a lower concentration. Even drier skin with isolated imperfections can benefit from a good, moisturizing, and barrier-strengthening skincare routine.

PHAs are an option for people with sensitive skin who often react irritably to AHAs or BHAs. They can be a good introduction to chemical exfoliation. However, for skin conditions such as rosacea or atopic dermatitis, their use should be considered individually and ideally under medical supervision, as even PHAs are not always well tolerated.

How to use acids correctly

For acids to achieve their full effect, proper application is essential. These five rules will help you avoid common mistakes:

1. Beginners should start slowly. Start with a low concentration and only 1 to 2 applications per week. Acids dissolve dead skin cells on the surface, and the skin needs time to get used to them. If you try too much too quickly, you risk redness, flaking, and a weakened skin barrier.

2. The correct order counts. Apply acids directly to dry skin after cleansing, before applying serums or creams. This allows them to work optimally. In exceptional cases , such as when very sensitive skin reacts strongly even with them, you can test applying a thin layer of moisturizer first (the "buffering method"). This will reduce the effect, but can make it easier to get started.

3. Never use multiple exfoliants at the same time. Using multiple exfoliants at the same time (e.g., an AHA toner plus a BHA serum and a PHA product) can quickly overwhelm the skin and weaken its barrier. Beginners are better off starting with just one product and observing their skin's reaction. Advanced users can also use combinations—carefully and in low concentrations—but should pay close attention to their skin's signals.

4. Listen to your skin's signals. A slight tingling or minimal dryness at the beginning is normal , but severe redness, burning, or flaky patches are not. In this case, stop immediately and Support your skin with soothing, moisturizing care before continuing with your application.

5. Sun protection is mandatory. Chemical exfoliants – especially AHAs – increase the skin’s sensitivity to light. Daily broad-spectrum sun protection is therefore essential - see also our detailed article on the correct Sunscreen . Without it, pigment spots can even become more pronounced—exactly the opposite of what is intended.

Avoid common mistakes

Many mistakes when handling acids can be easily avoided.

A common problem is the simultaneous use of several products containing AHA, BHA, or PHA. While this promises greater effectiveness, it leads to over-treatment, irritation, and a weakened skin barrier for most skin types. Therefore, it's recommended to always start with a single product and closely monitor your skin's reaction.

Increasing concentration too quickly is also a classic stumbling block. Even serums with 5% AHA or 2% BHA can have a noticeable effect for weeks. High-dose products with 15–20% AHA are available over the counter, but are more suitable for experienced users and occasional use, as they can quickly overwhelm the skin.

It is equally problematic to continue treating the skin with acids despite visible irritation . Slight dryness or a brief tingling sensation at first is normal, but redness, severe burning, or flaking patches are clear signals to take a break and soothe the skin. Skin care should support the skin—not burden it.

What you should look for in products

When purchasing, it's worth considering the concentration and formulation. For AHA, 5% is a good starting point for beginners, while 8–10% is suitable for advanced users. Products with higher concentrations above 15% to 20% are usually intensive peels that should only be used rarely and preferably under professional supervision, as they can be very stressful for the skin.

BHA is usually present in over-the-counter products at 1–2% and completely sufficient for effective use . PHA is commercially available at 3–7% and is very well tolerated.

The pH value also plays a role. For the acids to be effective, the formulation needs to be slightly acidic (around pH 3–4). High -quality products are designed for this, so you usually don't have to worry about it yourself.

When you should be careful

Not all skin tolerates acids equally well. Those suffering from a severely damaged skin barrier (more on this in this blog post ), open wounds, eczema, or active rosacea should proceed with caution and consult a dermatologist if in doubt. Caution is also advised during pregnancy and breastfeeding, especially with high-dose peels.

Conclusion

AHAs, BHAs, and PHAs are valuable tools in skincare when used consciously. It's crucial to choose the acid that suits your skin type, start with a low concentration, and give your skin time to adjust. With patience and consistent sunscreen , you can achieve visible improvements with acids—from smoother skin and fewer blemishes to a fresher, more even complexion.