Benzoyl Peroxide —
Oxygen Against Acne Bacteria

On the skin, benzoyl peroxide releases oxygen-rich free radicals that kill Cutibacterium acnes, the bacterium behind inflamed spots. It also loosens blocked pores a little. You may see it written as BPO or BP.

Because it works by oxidation rather than as an antibiotic, bacteria are not known to become resistant to it. That is why guidelines pair it with antibiotic treatment, to protect the antibiotic.

Many controlled studies support benzoyl peroxide for acne of mild to moderate severity, and it is recommended in the American Academy of Dermatology guidelines, alone or with a retinoid or antibiotic. On its own it is not enough for severe or scarring acne, which usually needs combined or oral treatment; see acne treatment.

Strengths usually run from 2.5% to 10%, and lower strengths often irritate less while helping about as much. Very dry or eczema-prone skin may do better with a short-contact wash, rinsed off after a short time. On the chest and back a wash reaches what creams cannot; see back and body acne.

It bleaches fabric, towels and hair, so apply it with care and use white linen. A non-comedogenic moisturiser, sunscreen and, where directed, a retinoid or niacinamide sit alongside it; add one new active at a time.

• A known allergy: avoid it. A few people develop allergic contact dermatitis.
• Eyes, lips and broken skin: keep it off.
• Pregnancy: check with a doctor first.

Dryness, peeling and stinging are common. Skin with rosacea or mite overgrowth often stings with it; that pattern needs a different plan.

Benzoyl peroxide acne products are generally regulated as medicines. Lower-strength gels and washes are usually sold in pharmacies; combinations with adapalene or clindamycin are prescription-only.