A quick lesson on why they work: Our skin skews slightly acidic in its pH, so commonly, acidic skin-care ingredients are heavy-hitters in every aspect of our regimens from adding hydration (a la hyaluronic acid) to brightening (care of L-ascorbic acid). "Because the skin mantle pH is between 4.5 and 6.2, products with pHs in this range perform the best," cosmetic chemist Ginger King explains. "If a product is on the alkaline side or greater than pH 7, skin will get rougher."
So it makes sense that when exfoliating, the same logic holds true; however, knowing the difference between the two top chemical exfoliant categories (AHAs and BHAs) will help you resolve specific skin qualms. Both types of acid work by breaking down the glue between cells to help remove dead skin cells while encouraging cell turnover, according to King. "The main difference, however, is solubility," she explains. "AHAs dissolve the bonds that hold dead skin cells together, and BHAs remove dead skin cells and unclog pores."
If all this cell-wall talk has images of Samantha Jones and her famous chemical peel on Sex and the City running through your mind, hold the phone. When used under a 10-percent concentration in a product, King tells me that they're quite safe while still being effective. And what's more: You don't even need to have that hurt-so-good sensation to tell they're working. "A big myth I hear frequently is if it doesn't burn, it's not working and that higher concentration of acids means the product's more effective," says New York City dermatologist Dennis Gross, MD. Because, even in lower concentrations, they're one of the most effective ways to exfoliate. All that intel and more, right this way.
Keep scrolling to get the down low on acids in skin care.
AHAs are derived from plant substances like sugar cane, milk, and grapes (which is why they're often referred to as fruit acids), explains Joyce Imahiyerobo-Ip, MD, a Boston dermatologist. "Unlike BHAs, they're actually water-soluble, water-loving molecules," she says. They function as an exfoliant by loosening the glue that hold skin cells together on the uppermost layers of the skin. "Doing this reveals rejuvenated and brighter skin," says Dr. Gross. "They also stimulate collagen, which helps to reduce the appearance of fine lines and wrinkles—which makes them good for aging skin." These acids are best tapped as frequently used anti-agers to help fend off signs of aging from hyperpigmentation and sun spots.
On the label, you'll see them as glycolic acid, lactic acid, mandelic acid, tantaric acid, and malic acid.
BHAs—which are beta hydroxy acids—take the exfoliation that AHAs do one step further. "Like AHA, BHA has an exfoliating effect," says Dr. Gross. "But it penetrates deeper to remove dead skin cells and unclog pores, and because of this, BHA can help your other products absorb better."
They're oil-based, making them particularly ideal for oily, acne-prone skin, especially whiteheads and blackheads, according to Dr.Imahiyerb-Ip. "BHAs are good at penetrating and dissolving clogged pores," she says. "They also have anti-inflammatory and antibacterial properties, which is why they're often found in acne products." These show up on labels as salicylic acid and citric acid.
What happens when you use them together?
While AHAs and BHAs are totally fine doing their own thing in your skin-care routine, they also come together quite nicely to deliver a souped-up result. Ultimately, a synergy of the two provides the best results—you just need to make sure they're okay with your skin type. Used alone, most skin types can tolerate the two individually; however, for those with the sensitive skin, a power-packed AHA-BHA combo might be too much. "As with any skin acid, those with sensitive skin may want to avoid AHAs and BHAs together as they may result in excessive skin dryness and redness," she says.
According to Dr. Gross, AHAs are work for all skin types, but because BHA is oil-soluble, meaning that it's job is to destroy oil and gunk, it's better for oily skin types, he says. And what's more, certain blends of acids fight different skin concerns. "For example, citric acid and malic acid are great for reducing the appearance of brown spots, lactic acid helps speed up cell renewal, helping lessen visible acne scars, and glycolic acid has amazing anti-aging benefits," he says.
As for how often to incorporate acids into your skin-care regimen, that's a matter of your skin's sensitivity level. "Depending on that," notes Dr. Gross, "you can use either everyday or at least 2 to 3 times a week."
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