Have you checked out a zit cream ingredient label before? A lot of action going on there. Salicylic acid… Tea tree oil… Benzoyl peroxide… Whosit… Whatsit… The list goes on. Sure, you may know all about the first two ingredients because they’re fun and sexy and everyone likes talking about them these days (see: this very site), but benzoyl peroxide? Eh. So boring. So clinical. So...effective? So…???? What does this ingredient actually do? Sanitize zits? Lighten pimples like hair dye? Just sound weird? Well, ITG enlisted the help of Dr. Maryann Mikhail of Spring Street Dermatology to find out.

So what is benzoyl peroxide?

Like the liquid in the dark brown bottle that you use to clean cuts—hydrogen peroxide—benzoyl peroxide is an antibacterial. “It’s cytotoxic,” says Dr. Mikhail, “meaning it kills the bacteria cells.” Because it isn’t water-soluble, benzoyl peroxide (also called BPO) actually forms a little film on the skin, making it less abrasive and more effective at treating acne. It’s extremely good at shrinking blackheads and whiteheads. Studies have shown that BPO works better on breakouts than other acne-fighting ingredients, like azelaic acid and topical antibiotics, and is just as safe to use as topical retinoids. It’s different from something like salicylic acid, another popular pimple remedy, because AHAs and BHAs mainly exfoliate, reduce inflammation, and remove dirt on the surface. The oxygen in BPO penetrates deep into the pore to actually treat the zit from the inside, out.

If I have sensitive skin, can I use it? What if I have dry skin or rosacea?

“It’s a little tricky because it kind of depends on how you’re using it,” says Dr. Mikhail. If your skin is super sensitive or you have rosacea, BPO may not be the ingredient for you—or at least not for everywhere. Spot treating it one thing; masking your entire face with it is quite another. If you know your skin is sensitive or dry, try using BPO in a small, inconspicuous area. If it feels like too much, stop!

OK, you said it was antibacterial. If I use it often, will I build up a resistance?

Not only will you not build up a resistance to BPO, it actually prevents resistance when used with a topical antibiotic. “If you have benzoyl peroxide in the routine, it prevents antibiotic resistance. Actually, we very rarely prescribe topical antibiotics without benzoyl for acne,” says Dr. Mikhail. Dermatologists don’t know why it happens, but they know it works.

Great! So which benzoyl peroxide products can I get next time I’m at CityPharma?

Actually, benzoyl peroxide is only available by prescription in Europe.

Wait, why?

It’s just the law! But this doesn’t mean it’s unsafe. Several studies, including ones cited by the European Commission, show that benzoyl peroxide is safe to use on skin in low concentrations. In the US, BPO is available over the counter in concentrations of 2.5%, 5% and 10%. If you’re reading from Europe, you’ll have to talk about it with your dermatologist. Like any active skincare product, you should follow with SPF, avoid contact with lips, eyes, and mouth, and stop using it if your skin becomes too irritated.

So, I read that BPO might bleach my sheets if I sleep with zit cream on my face.

You read right! Might be time to invest in some very adult, white sheets as a precaution.

Oh! Is it going to bleach my skin?!

Absolutely not!

Why does it bleach one and not the other?

Skin is constantly producing new pigment thanks to melanocytes, pigment-producing (melanin) cells in the body. An enzyme called tyrosinase signals this constant melanin-producing operation. In order for skin-bleaching products to be effective, they have to block the body’s tyrosinase activity. Think of a skin-lightening ingredient like hydroquinone—it’s toxic to tyrosinase and stops melanin production. BPO doesn’t bleach skin because it doesn’t respond to tyrosinase. It’s a completely different situation for fabric and hair, which are more vulnerable to BPO because neither are constantly producing more “pigment,” unlike skin. To be safe, try not to apply before bed or let your spot treatment touch your eyebrows.

Pivoting here—will it cause hyperpigmentation?

Hyperpigmentation after a breakout is called post-inflammatory hyperpigmentation (PIH), and is your skin’s natural reaction to irritation. You may get a dark mark on your skin after a zit has gone away, or after an old bug bite heals. High concentrations of BPO can be irritating to skin, which can also trigger hyperpigmentation. “You’re not getting hyperpigmentation from BPO, you’re getting it from the irritation or contact dermatitis it can cause,” clarifies Dr. Mikhail. You can avoid irritation by using a product with a lower concentration of BPO, or you can just use the product you already have less frequently.

Can I put it on my...face?

Yep.

...Body?

Double yep. “I think where it’s really useful is back and butt acne—the breakouts that happen from occlusion, like when you work out and sweat,” says Dr. Mikhail. But you may want to use different forms of it for different areas. Remember that if you put a BPO spot treatment on your chest or back, it could end up bleaching your clothing. You’re better off with a cleanser that includes some concentration of BPO. You can look for one with a slightly higher concentration, because the skin on your body is less sensitive than the skin on your face.

Where does it fit in my current skincare routine?

Dr. Mikhail recommends you keep it simple: “You would wash your face with a gentle cleanser first, then apply the benzoyl peroxide—no more than a pea-sized amount—then use moisturizer and sunscreen.” Any serums you use should go on after BPO. Proceed with caution when adding in other actives—retinol, exfoliating acids and BPO are all pretty serious ingredients. You can still keep them in your routine, but try spacing them out to avoid irritation—BPO should be applied in the morning so it doesn’t bleach your sheets, and a BHA, PHA, or AHA liquid exfoliant can be used at night. “You also wouldn’t want to use it with anything oil-based,” says Dr. Mikhail, “because that would be counterproductive.” Save the face oils for night, and you’re good to go.

Are you going to tell me to use SPF again?

No. Kidding—were you even paying attention? Always yes—especially when your face is loaded with active ingredients. “Proper use of sunscreen, and at least SPF 30 or higher, would be ideal,” says Dr. Mikhail. But you knew that by now.

Photo via ITG