“Beetle juice” is the common nickname for cantharidin, a blistering agent derived from blister beetles that doctors apply directly to molluscum bumps to destroy them. It became the first FDA-approved treatment for molluscum contagiosum in 2023, under the brand name Ycanth, and is approved for adults and children ages 2 and older.
Molluscum contagiosum is a viral skin infection that causes small, firm, dome-shaped bumps. It’s extremely common in children and usually harmless, but the bumps can persist for months or even years and spread easily. Cantharidin offers a way to clear them without cutting, scraping, or freezing.
Where Cantharidin Comes From
Cantharidin is a natural chemical produced by blister beetles, insects in the family Meloidae. The most well-known species is the Spanish fly (Lytta vesicatoria), but several North American species also produce it. The beetles secrete cantharidin as a defense mechanism. When concentrated and applied to skin, it acts as a vesicant, meaning it causes blisters to form.
Dermatologists have used cantharidin for decades to treat warts and molluscum, but until recently it was only available as a compounded (pharmacy-mixed) solution without formal FDA approval. The standardized version, Ycanth, changed that, giving providers a consistent, regulated product.
How It Destroys Molluscum Bumps
When cantharidin is absorbed by skin cells, it triggers the release of enzymes that break apart the structures holding cells together. Think of it like dissolving the glue between bricks in a wall. The top layer of skin separates from the layer beneath, and a fluid-filled blister forms directly under the molluscum lesion. As the blister rises, it lifts the infected tissue away from healthy skin. Once the blister heals, the virus-containing bump is gone.
This process is intentional. The blister is the treatment working, not a complication.
What a Treatment Visit Looks Like
Cantharidin is applied only by a healthcare provider, never at home. Using a specialized applicator, the provider places a tiny droplet of the solution directly onto each molluscum bump and spreads it to cover the lesion. The solution may turn the treated skin a violet color temporarily.
After application, you leave the solution on the skin for 24 hours, then wash it off gently with soap and water. During those 24 hours, you should avoid touching the treated spots, applying any other products like lotion or sunscreen over them, and exposing the area to open flame (the solution is flammable until washed off). If a child is being treated, make sure they don’t scratch, rub, or let pets lick the area.
Most treatment plans involve one session every three weeks for up to four total treatments. Each visit addresses whatever active bumps are present at that time.
Clearance Rates and What to Expect
In the two large clinical trials that led to FDA approval, 50% of patients treated with cantharidin achieved complete clearance of all molluscum lesions by day 84, compared with just 15% in the placebo group. Published clearance rates across various studies range widely, from about 15% to 100%, depending on the number of lesions, the number of treatment sessions, and the specific formulation used.
The takeaway: most people see significant improvement, but it often takes multiple sessions. Some bumps clear after one treatment, while others need a second or third round. New bumps can also appear between visits since the virus may have already spread before treatment started.
How It Compares to Freezing and Scraping
The main alternatives for removing molluscum are cryotherapy (freezing with liquid nitrogen) and curettage (scraping off bumps with a small instrument). Both have slightly higher overall clearance rates, ranging from 70% to 100%, but they come with significant downsides, especially for kids.
Freezing and scraping hurt during the procedure itself. They require a child to sit still while each bump is individually treated, which can be distressing. Both carry a real risk of scarring and permanent skin color changes at treatment sites. Cantharidin, by contrast, is painless at the moment of application. The discomfort comes later, at home, as blisters form. For young children who are anxious about doctor visits, that tradeoff can make a meaningful difference. The risk of scarring with cantharidin is also considered negligible compared to physical removal methods.
Side Effects and Risks
Blistering is the most common side effect, and it’s expected. In clinical studies, 92% of patients developed mild to moderate blisters at treatment sites. About 37% experienced redness around the area. Other reported side effects included mild pain (14%), a burning sensation (10%), itching (6%), and temporary changes in skin color at the treatment site, either darker or lighter than surrounding skin (8%). Severe blistering occurred in roughly 2.5% of patients.
The skin color changes typically fade over weeks to months but can be more noticeable in people with darker skin tones. If severe pain, large blisters, or signs of infection develop before the 24-hour mark, you should wash the solution off early with soap and water and contact your provider.
After washing off the cantharidin at the 24-hour mark, use gentle technique. Avoid rough washcloths and don’t scrub the area. The blisters will typically dry and heal on their own over the following days.
Who Should Not Use It
Ycanth is not approved for children under 2 years old. Because cantharidin works by creating controlled skin damage, it should not be applied to areas where blistering could cause serious problems, such as near the eyes or on mucous membranes. If the solution gets in the eyes, flush with water for 15 minutes and seek medical attention immediately.
Your provider will determine whether cantharidin is appropriate based on the location and number of lesions, your child’s age, and any other skin conditions that might complicate healing.