polyhexamethylene biguanide, used in mouthwashes, swimming pool sanitizers and contact lens cleaning solution. Kills everything, doesn't hurt people...which is what they told us about pHisohex hand cleaner until folks with large areas of non-intact skin absorbed enough of it to seize, and what they told us about the hard plastic nalgene drinking bottles, and the Ford Pinto...forgive it, just the cynicism of an old, disillusioned nurse. The new kerlix is probably just fine.