The present invention provides compositions comprising at least one cation selected from the group consisting of Ga.sup.+3 and La.sup.+3, that effectively inhibit the discharge of nematocysts or polar capsules. The compositions described herein are effective at inhibiting nematocyst or polar capsule discharge when applied topically prior to exposure to nematocysts. The present invention further provides methods for inhibiting the discharge of nematocysts or polar capsules, comprising applying to the skin of a subject prior to contact with the nematocyst or polar capsule a compositions comprising at least one cation selected from the group consisting of Ga.sup.+3 and La.sup.+3. Thus, the present invention provides protection for swimmers, divers and fishermen, from nematocysts or polar capsules discharged from stinging marine organisms such as Cnidaria and Myxozoa.