Cantharidin is typically left on the skin for 2 to 6 hours, depending on where it’s applied and what it’s treating. The official prescribing information says 24 hours for molluscum contagiosum, but in clinical practice, most providers instruct patients to wash it off much sooner to control blistering and reduce the risk of complications.
Timing by Body Location
The single biggest factor in how long cantharidin should stay on is where on your body it was applied. Thinner, more sensitive skin reacts faster and blisters more aggressively, so it needs less contact time.
- Trunk and extremities (arms, legs): 4 to 6 hours
- Hands and feet (common and plantar warts): 4 to 6 hours
- Face, neck, and genitals: 2 to 4 hours maximum
Sensitive areas like the face and skin folds carry a higher risk of scarring, so providers often start at the shorter end of that range and adjust upward at future visits based on how your skin responded. If your provider gave you a specific number, follow that over any general guideline.
Molluscum vs. Warts
Molluscum contagiosum lesions are superficial and generally respond to shorter contact times. The formal dosing guidance lists 24 hours, but many dermatologists use the 4 to 6 hour window (or 2 to 4 hours on the face) because molluscum doesn’t require the deep tissue penetration that thick plantar warts do.
Warts, especially plantar warts on the soles of the feet, sit under a thicker layer of skin. For these, providers sometimes use a stronger compound that combines cantharidin with other peeling agents. Even with this stronger formulation, the typical contact time remains 4 to 6 hours. The added ingredients do the extra work, not extra time on the skin.
How to Wash It Off
When your time is up, wash the treated area with soap and water. The Mayo Clinic specifically advises against using a washcloth, abrasive material, or vigorous rubbing, since the skin underneath is already irritated and scrubbing can be painful. Gentle lathering with your hands and warm water is enough to remove the dried film.
If you were given a bandage or dressing over the treatment site, some clinics recommend leaving it in place for up to three days before washing. Follow whatever instructions your provider gave at the visit, since protocols vary depending on the formulation used.
When to Wash It Off Early
Some blistering is the entire point of cantharidin. It works by separating the top layer of skin from the layer beneath it, lifting the wart or molluscum lesion off with the blister roof. But the process shouldn’t be agonizing. If you experience intense pain, significant swelling beyond the treated spot, or the burning sensation becomes hard to tolerate before your target time, wash the area off immediately with soap and water. Leaving it on longer than necessary doesn’t improve results. It just increases the chance of a larger, deeper blister or skin discoloration.
What Happens After Treatment
Within a day or two of application, a blister forms at the treatment site. This is expected and means the treatment is working. About 92% of patients in clinical studies experienced mild to moderate blistering. Around 37% had redness at the site, and smaller numbers reported mild pain (14%), burning (10%), or itching (6%).
The blister typically crusts over and falls off within 4 to 5 days, leaving a shallow, superficial wound underneath. You can apply petroleum jelly or an antibiotic ointment to the raw area twice a day until it heals, which takes most people 5 to 10 days total from the treatment date. For warts specifically, some providers recommend applying an over-the-counter salicylic acid product to the healed base daily for about a week afterward to prevent regrowth at the edges.
About 8% of patients develop temporary changes in skin color at the treatment site, either lighter or darker patches. These usually fade over weeks to months but are worth knowing about, particularly on darker skin tones where pigment changes tend to be more visible.
Multiple Treatments Are Common
One session often isn’t enough. For molluscum, a study of 300 children found that an average of about 2 visits cleared all lesions in 90% of cases. Warts tend to be more stubborn. In a real-world study tracking both children and adults with cutaneous warts, 86.5% of children achieved complete clearance, compared to 62.7% of adults. Nearly two-thirds of children needed only 1 to 3 treatments, while the majority of adults required 4 or more sessions. Treatments are typically spaced 3 to 4 weeks apart to allow the skin to fully heal between applications.
Severe complications are uncommon. About 2.5% of patients in clinical studies developed severe blistering, and rare side effects included mild infection, irritation, and bleeding. If the blister becomes cloudy, streaked with red, or increasingly painful days after treatment rather than improving, that can signal a secondary infection worth getting checked.