Cantharidin, a type of terpenoid, is a chemical compound secreted by many species of blister beetle, and most notably by the Spanish fly, Lytta vesicatoria. The false blister beetles, cardinal beetles and soldier beetles also produce cantharidin. It is a poisonous substance, acting as a blister agent, and can cause severe chemical burns, but these same properties make it effective as a topical medication. Cantharidin is absorbed by the lipid membranes of epidermal cells, causing the activation or release of serine proteases, enzymes that cleave (break) peptide bonds in proteins. This causes the disintegration of desmosmal plaques, cellular structures involved in cell-to-cell adhesion, leading to detachment of tonofilaments that hold cells together. The process leads to the loss of cellular connections (acantholysis) and ultimately blistering of the skin. Lesions heal without scarring.
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