Polyaminopropyl Biguanide

Polyaminopropyl biguanide (PHMB) is a broad-spectrum antimicrobial preservative/disinfectant typically used at low concentrations (about 0.01–0.1% in cosmetics/cleansers; higher in some antiseptic uses). Despite low use levels, clinical and post-market data show it can cause irritant dermatitis and, in a minority of users, allergic contact dermatitis—risk that increases on compromised skin barriers (eczema, post-procedure) and with leave-on exposure. Given its biocidal mechanism and documented reactivity in sensitized populations, I score it as moderate irritation potential where patch testing is prudent for highly sensitive skin. Safety Notes: Polyaminopropyl Biguanide (PHMB) is used primarily as a preservative/antimicrobial in consumer skin-cleansing and personal care products, commonly appearing at very low “booster” levels around 0.0001–0.01% (especially in rinse-off cleansers and wipes) and more typically around ~0.02–0.1% where it is the main preservative system. The upper end in OTC consumer-available products reaches about 0.3% in some high-antimicrobial cleansing/wipe-type formulations, but higher levels are generally uncommon due to irritation/sensitization risk and regulatory scrutiny; leave-on facial products tend to stay on the lower half of the range versus rinse-off.