Found in nature and produced by certain beetles, cantharidin is a substance that produces blisters on skin. As the chemical can break down skin cells so well, scientists have developed a use for it in removal of warts and other undesirable skin growths. Basically, after a doctor paints on the chemical to the growth, it destroys the excess tissue and the growth falls off. Possible side effects include blistering of healthy skin, and some people have more sensitivity to cantharidin than others. As of 2011, cantharidin has not been extensively studied, and may not be approved for use in certain regions of the world.
Blister beetles are the natural source of cantharidin, and they produce this destructive chemical as a self-defense measure against other organisms. When humans come into contact with the beetle, and it releases the chemical onto the skin, the skin blisters, hence the name blister beetle. This blistering capacity of the cantharidin make it potentially useful for removing unwanted skin growths.
Warts, verrucas and infectious growths on the skin such as molluscum contagiosum can all be removed using cantharidin application procedures. Commonly, this form of growth removal involves liquid nitrogen or salicylic acid application, which help to break down the cells in the growth so that the growth falls off. Cantharidin has the same effect, and as it appears to leave little scarring, may even be more suitable for treatment of skin that is often seen, like the back of the hands or the face.
Normally, a doctor applies the cantharidin onto the growth so it covers the whole growth. Then he or she covers over the area with a bandage or a plaster so the chemical can work on the excess cells. The blistering effect of the chemical destroys the cells and when the area is dry, the growth can be scraped off in another doctor's appointment. Sometimes more than one treatment is necessary to remove the entire growth, with a week or more between treatments.
Patients may suffer localized pain from the blister during the treatment, and the skin may be sore for up to a week after. During this time, the pain may be alleviated with painkillers, or the patient can apply cold water to the skin to ease the soreness. Some types of skin growths are not suitable for treatment with this chemical, and these include any warts on mucosal surfaces, hairy warts or moles.