Cantharidin is a substance derived from the blister beetle Cantharis vesicatoria. The Chinese have used this ancient medicine for thousands of years for a number of maladies. In the 1950’s it was used in the US and other westernised countries to treat warts and molluscums.
How does Cantharidine work and what is it used for?
Cantharidin is a vesicant that causes a blister to form on the wart or growth. This action lifts the wart off the skin and after a few days when the blister has dried the wart will come off. The action of cantharidin does not go beyond the epidermal cells (the superficial layer of skin), the basal layer remains intact hence no scarring. Cantharidin is sometimes effective in treating common viral warts and very frequently effective for molluscum contagiosum. Both are viral skin infections that result in small, harmless skin growths.
How to use Cantharidine
Because of the toxic potential of cantharidine it should only be used topically and in a professional clinic setting, applied to the lesions by your dermatologist.
Cantharidin should be used as follows.
- Firstly your doctor will shave the wart (this is not necessary for molluscum).
- Cantharidin (formulated with substances that create an oily or colloidal film) is accurately applied to the wart or molluscum.
- The liquid is allowed to dry and then covered and sealed with nonporous plaster for 4-6 hours.
- The plaster should then be removed and the area washed with soap and water. This may be uncomfortable for your young children.
- Within 24 to 48 hours a blister will form.
- Over the next few days the blister will dry and the lesion may fall off. If necessary the blistered lesion can be snipped off near the base (local anaesthetic may be required).
- Healing is normally complete within 7-10 days.
- Meanwhile, do not scratch or pick the scabs.
- Resistant warts or new molluscum lesions may require a repeat treatment.
Side Effects of Cantharidin
Usually the application of cantharidin on the wart does not hurt and therefore an excellent treatment method for young children and babies, but the resulting blister can sometimes be uncomfortable when removing the plaster. In a small number of patients, a ring of small atellite warts surrounding the original wart may appear after cantharidin treatment. However, this complication can just as likely occur with other wart removal therapies.