Chlorhexidine is a chemical antiseptic. It is effective on both Gram-positive and Gram-negative bacteria. It has both bactericidal and bacteriostatic mechanisms of action, the mechanism of action being membrane disruption, not ATPase inactivation as previously thought. It is also useful against fungi and enveloped viruses. Chlorhexidine is harmful in high concentrations, but is used safely in low concentrations in many products, such as mouthwash and contact lens solutions.