Painless application and the absence of instruments makes it especially useful for treating children. It is not recommended for use near eyes, on mucous membranes, or in ano-genital, or intertriginous areas. Cantharidin is a strong vesicant. Do not use near eyes, on mucous membranes, or in ano-genital area. Avoid use in intertriginous sites due to problems with spreading and body occlusion which often lead to more intense, painful reactions.
Patients vary in their sensitivity to cantharidin.
A more intense reaction is to be expected in patients with fair skin and blue eyes. Do not treat large areas or multiple lesions before establishing the sensitivity of the patient. Do not re-apply to the same lesion more than once per week. Defer second treatment if inflammation is intense. In rare cases tingling, burning or extreme tenderness may develop.