Cantharidin

Cantharidin is a terpenoid vesicant toxin originally isolated from blister beetles (notably *Lytta vesicatoria*). It is used medically as a topical treatment for molluscum contagiosum and viral warts due to its ability to induce acantholysis and blistering confined to epidermal cells. Upon application, it is absorbed by the lipids in the membranes of keratinocytes, triggering the release of neutral serine proteases that degrade desmosomal cell adhesion structures. This results in intraepidermal blister formation that helps detach viral lesions without scarring. Cantharidin is highly toxic if ingested and is classified as an extremely hazardous substance. In dermatology, it is usually formulated in low concentrations, alone or with other agents such as salicylic acid and podophyllin, but therapies must avoid mucosal, ocular, and oral contact due to systemic toxicity.

Other names

Spanish fly (as a crude extract or historical substance)Cantharis vesicatoria toxin

Absorbed by the lipid membranes of epidermal keratinocytes, leading to activation and release of neutral serine proteases, which break down desmosomal plaques (structures responsible for cell-to-cell adhesion in the epidermis), resulting in selective acantholysis and blister formation. Cantharidin is also a potent inhibitor of protein phosphatase 2A, which may contribute to additional biological effects (e.g., in vitro anticancer activity).