As acids become more and more prevalent in skin care, how to use them can seem even more confusing. Not only are there many different types of acids to choose from, but there are also varying percentages of acids you can use. Should you go for a 15% glycolic acid peel, or keep it conservative with a 5% glycolic acid-infused formula? Do you need 0.5% salicylic acid or 2%? Here, we consulted with Dr. Craig A. Kraffert, board-certified dermatologist and founder of Amarte Skin Care to help explain commonly found percentages of acid in skin-care formulas and how they may help you achieve  your skin-care goals. What percentage of common alpha-hydroxy-acids (AHAs) and beta-hydroxy-acids (BHAs) are typically found in skin-care products? Glycolic acid is a popular AHA because it has a small molecule size that allows it to penetrate deep into skin’s surface to reveal a smoother, brighter, more even-toned and more youthful complexion. “Typical concentrations range from 6 to 25%,” says Dr. Kraffert. Another common AHA is lactic acid. Because it’s a bigger molecule than glycolic acid, it has less potential for sensitizing skin. In addition to its exfoliating properties, it can also help skin retain moisture. Dr. Kraffert notes that you can often find it in concentrations of 6 to 12%. Salicylic acid, a BHA, is oil-soluble (AHAs are water-soluble), making it commonly used as an acne treatment. “Concentrations range from 0.5 to 2%,” says Dr. Kraffert. “Salicylic acid is a profound exfoliant and may irritate skin, especially at higher potency.” What acid percentage should you start with?There’s no one-size-fits-all approach to acids — “it’s all about tolerability,” says Dr. Kraffert. However, it’s always a good idea to start small. “Stronger products will tend to more profoundly affect the appearance of skin renewal via exfoliation but they also tend to be less well-tolerated,” he says. If you choose a concentration that’s too high, you can experience redness, tenderness and even pain. Over-exfoliating can also dehydrate your skin and result in dryness, flakiness and breakouts. Working your way up will help you determine what level of exfoliation your skin can safely tolerate. “With repetitive chemical exfoliation, skin adapts,” Dr. Kraffert says. “Once adapted, stronger concentrations are tolerated and may be necessary to see results similar to those seen earlier in a treatment cycle at lower concentrations.” If you notice any of the side effects mentioned above, it’s time to take a break or drop back down to a lower concentration. It’s always advisable to consult with your dermatologist before incorporating new ingredients, such as acids, in your skincare routine and use products as directed.. 
