What Are AHAs and Glycolic Acid? Proper Use and Risks

What glycolic acid does: It can help loosen the bonds that hold dead cells on the very top of the skin, reducing roughness, dull appearance, and mild tone unevenness. The framework accepted for home use is a concentration of 10% or below, a pH of 3,5 or above, and daily sun protection. Start with 1-2 evenings a week. AHAs make the skin sun-sensitive; this sensitivity disappears about a week after the product is stopped. It is not considered a solution for acne or melasma on its own.

Who's who in the AHA family?

AHA (alpha hydroxy acid) is the name of a group of water-soluble acids. Glycolic acid is the smallest molecule in the family, so it penetrates the upper layer more easily and feels strong. Its other members behave differently, and lumping them all together as "acid" is misleading.

The oil-soluble cousin of AHAs, salicylic acid, is in the BHA group and is known for reaching inside the pore. AHAs work on the skin's surface. If your goal is roughness and dullness, AHA is a more sensible starting point; if it is blackheads, BHA is.

What does glycolic acid do? How long is the evidence?

It speeds shedding by loosening the bonds between cells. This effect is called exfoliation and has been well demonstrated. The main debate is how much it changes appearance.

• Sun damage appearance: In a double-blind, base-controlled study with 74 women, a cream with 8% glycolic or 8% lactic acid was used for 22 weeks. The overall improvement of at least one degree in the facial area was 76% and 71%, and 40% in the base cream. On the forearm, lactic acid also showed a difference in spotted discoloration and roughness. The researchers described the effect as 'modest'. This is a good measure of what to expect from a home product.
• Dark tone and spots: With over-the-counter products, several months may be needed for a difference in brightness and tone. For clear spots and melasma, clinical peeling or a doctor's treatment is usually considered.
• Collagen: It is reported that collagen production can be supported with high concentrations and long-term use. Do not expect to see this with a low-concentration home product, especially in a short time.
• Acne: In a broad systematic review of acne, for AHAs only one small study was found, comparing a glycolic acid peel alone with another peel, and the certainty of the result is low. It may support pore cleansing, but it has not been studied enough as an acne treatment.

Realistic expectation: a smoother feel in a few weeks and a more even appearance in a few months. It is not enough for deep wrinkles, deep scars or intense spots. Options for acne scars should also be evaluated separately.

A percentage alone is not enough: Concentration and pH are read together

Four things determine how strong a product is: the type of AHA, the concentration, the pH, and the other ingredients in the formula. The same 10% can be gentle in a high-pH product and much harsher in a low-pH product, because the active portion of the acid increases at low pH. So saying '5% is mild' is not always correct.

The limits in the first two lines are the result of an independent expert panel that reviewed cosmetic ingredients; in every country they may not be a legal requirement. A product survey conducted in the US also found two products below the recommended pH limit. The practical result is this:

• If the label does not state a percentage or pH, use the product at the lowest frequency.
• Be careful with high-concentration home products sold as 'peel'; if the concentration is well above 10%, do not use it on your own.
• Check whether the product is rinse-off or leave-on. Acid in a cleanser stays in contact for only a very short time.
• Do not try to buy glycolic acid powder or pure solution from the internet and dilute it yourself.

Cleanser, toner, serum: Same acid, different contact

Consider the percentage stated on the product together with how long it stays on the skin. The table below is a guide derived from this logic and does not give a fixed limit.

If glycolic acid will also be applied to areas such as the chest and neck, be careful. A product you use without problems on your face may act harsher than expected on these thin-skinned areas. Lactic acid, on the other hand, is often used on the arms' rough follicle bumps (keratosis pilaris) and in body products; since it is an AHA, it also needs sun protection there.

Sun sensitivity: The one-week rule

This is AHA's most clearly demonstrated side effect, and applying it in the evening does not eliminate it. The effect appears when the skin goes into the sun the next day. In controlled studies, after four weeks of regular use, the skin's sensitivity to redness from UV light increased by about 18%, and its predisposition to cellular damage on average doubled. The good news is that no difference remains a week after stopping the product. This is also why the label warning 'protect yourself from the sun while using it and for a week after stopping' is recommended.

1. Every morning: Apply a broad-spectrum sunscreen of at least SPF 30. Understanding the SPF value makes choosing easier.
2. During the day: Reapply the cream every 2 hours, and after sweating or swimming.
3. Protect yourself: Hat, shade and protective clothing. The difference between UVA and UVB explains why it is needed even on cloudy days.
4. Holiday plan: Stopping AHA use at least one week before an intense sunny holiday is a sensible precaution derived from this data.

Sample plan for the first eight weeks

Starting with 1-2 evenings a week is an established recommendation; the next steps are a starting point derived from it. If the product's label says otherwise, follow the label.

Some skin eventually tolerates every night, but that is not the goal. If you are getting results with a low frequency, there is no need to increase it. The sequence is simple: cleanse, acid, moisturizer. Sunscreen in the morning.

What should not be used on the same evening?

• Retinol: Retinol on the same night increases dryness and peeling. Separate them onto different nights; do not use them together in the first weeks.
• Salicylic and lactic acid: Adding a second exfoliant on the same evening is unnecessary.
• Vitamin C: Use the vitamin C serum in the morning; do not combine them in the same layer at the start.
• Mechanical peels and brushes: Do not do them on the same day; acid already thins the upper layer.
• Niacinamide and hyaluronic acid: They can generally be used together and may help balance dryness. Still, add new products one at a time.

Who should be careful?

• Sensitive and dry skin: High likelihood of irritation. Consider starting with lactic acid or a lower concentration.
• Rosacea, eczema, active infection: Ask a dermatologist before use. Irritation may increase on skin that has not healed.
• Sunburn, cut or open wound: Do not apply to that area; wait until the skin has fully recovered.
• Dark skin: Dark spots may develop after irritation. Proceed slowly; if darkening begins, stop the product and see a doctor.
• Pregnancy and breastfeeding: Low-concentration products are said to be generally considered safe due to minimal absorption, but there are no studies in pregnant women. Consult your obstetrician or dermatologist before use. Also, do not undergo a clinical peeling plan during this period without discussing it with your doctor.

How do you know it is too much?

In the US, between 1992-2004, among 114 adverse reports related to AHA skin products, burning (45), rash (35) and swelling (29) were the most frequent. Serious reactions were most often seen with strong exfoliating products. The number is small, but reporting systems capture only some of the events. Look for these signs on your own skin:

• A moisturizer that normally doesn't sting starts to sting
• Constant tightness and skin that looks shiny and thin
• Flaking, small cracks
• Newly appearing small pimples or itching
• Areas that darken at the application site

If this happens, stop the acid, switch to a gentle cleanser and a thick moisturizer, and continue sunscreen. After a few weeks, try again at a less frequent rate, only once the skin is completely calm. If there are blisters, severe burning, swelling, or redness that does not go away, rinse off the product immediately and see a dermatologist.