The binding of positively charged species to a membrane (to the negatively-charged head-groups of phospholipids) can alter the susceptibility of the membrane to oxidative damage. This can be seen as either an enhancement or an inhibition of the rate of lipid peroxidation. Several metal ions such as Ca2+, Co2+, Cd2+, Al3+, Hg2+ and Pb2+ alter the rate of peroxidation in liposomes, erythrocytes and microsomal membranes, often stimulating the peroxidation induced by iron ions.