Mohs surgery (often spelled phonetically as “Moe’s surgery”) is a precise technique for removing skin cancer one thin layer at a time. Each layer is examined under a microscope immediately, and the surgeon keeps going until no cancer cells remain at the edges. The result is a procedure that can cure up to 99% of skin cancers while removing as little healthy tissue as possible.
How the Procedure Works
The process starts with local anesthesia to numb the area, similar to what you’d get at the dentist. Once the area is numb, the surgeon uses a scalpel to remove the visible portion of the cancer along with a thin layer of tissue underneath and around it. That tissue sample gets mapped, color-coded, and sent to a lab right there in the office for immediate analysis.
Here’s what makes Mohs different from a standard skin cancer removal: the tissue is sliced horizontally, which allows the surgeon to examine 100% of the tumor’s edges under a microscope. In a standard excision, the tissue is sliced vertically (like a loaf of bread), which only captures about 2% of the margin. That difference in how the tissue is processed is the reason Mohs is so much more accurate.
If the microscope reveals cancer cells still present at any edge, the surgeon removes another thin layer from only that specific area. You wait in the office while each layer is processed and analyzed, then return for the next round if needed. This cycle repeats until the margins are completely clear. Most procedures involve one to three rounds, though complex cancers may require more. The entire process typically takes several hours, with most of that time spent waiting between layers rather than in actual surgery.
What Mohs Surgery Treats
Mohs is used primarily for basal cell carcinoma and squamous cell carcinoma, the two most common types of skin cancer. It’s also used in certain cases of penile cancer, lip cancer, and soft tissue sarcomas of the skin.
Not every skin cancer needs Mohs. The procedure is reserved for situations where the cancer has a high risk of coming back or where preserving as much healthy tissue as possible really matters. That includes cancers located in what dermatologists call the “H zone” of the face: the central face, eyelids, eyebrows, nose, lips, chin, ears, and the skin around the ears. It’s also recommended for cancers on the hands, feet, ankles, nail beds, and genitalia, where losing extra tissue could affect function or appearance.
Certain tumor features push a cancer into the high-risk category as well. These include aggressive growth patterns seen under the microscope, cancers that have grown into nerves, tumors thicker than 2 millimeters, and cancers that came back after a previous removal. Patients who are immunocompromised or have genetic conditions that predispose them to skin cancer are also strong candidates.
Cure Rates and Effectiveness
Mohs has the highest cure rate of any treatment for basal cell and squamous cell carcinomas. For primary basal cell carcinomas in high-risk areas like the face, the cure rate is around 98 to 99%, compared with 93 to 95% for standard surgical excision. The difference comes down to that comprehensive margin analysis: because the surgeon can see exactly where cancer remains, very little gets left behind.
For high-risk squamous cell carcinomas, outcomes are also strong. A study of 581 high-risk squamous cell cancers treated with Mohs found a five-year local recurrence-free survival rate of 96.9% and a disease-specific survival rate of 95.7%. These results were better than historical outcomes reported with other treatment methods, even using strict staging criteria.
Beyond cure rates, Mohs produces smaller wounds. Research comparing the two approaches found that cancers treated with Mohs left a median surgical defect of about 116 square millimeters, compared to nearly 188 square millimeters with standard excision. A smaller wound means simpler reconstruction and, in many cases, less visible scarring.
Who Performs the Surgery
Mohs surgeons are dermatologists who have completed an additional one- to two-year fellowship specifically in micrographic surgery and dermatologic oncology. These fellowship positions are accredited through organizations like the Accreditation Council for Graduate Medical Education in the United States, and the selection process is highly competitive. The surgeon acts as both the cancer surgeon and the pathologist, personally examining each tissue layer under the microscope rather than sending it to a separate lab.
Closing the Wound
Once the margins are clear, you’re left with an open wound that needs to be addressed. The approach depends on the size and location of the defect. Small wounds in areas where scarring isn’t a major concern can sometimes be left to heal on their own, a process that may take four to six weeks. Larger or more visible wounds are typically closed with stitches.
For bigger defects, the surgeon may use a local flap, which involves repositioning nearby skin to cover the wound, or a skin graft taken from another part of the body. In some cases, a staged reconstruction using tissue expanders may be recommended. When the cancer is on the face, reconstruction is often performed the same day by the Mohs surgeon or a facial plastic surgeon to get the best cosmetic result.
Recovery and Healing
Most people manage post-procedure discomfort with acetaminophen (Tylenol) alone. Swelling and bruising around the surgical site are normal and generally improve within a week, though the location of the surgery can affect where that swelling shows up. Surgery on the forehead or nose can cause the eyelids to swell noticeably, sometimes nearly closing them. Surgery on the chin or jawline can send bruising down the neck. Applying an ice pack for 20 minutes each hour while awake during the first 48 hours helps reduce both.
A little blood or fluid seeping through the bandage is normal. Active bleeding that soaks through the dressing is rare but should be managed with firm pressure using dry gauze for 20 minutes. Infection, significant bleeding, and serious pain are all uncommon after Mohs.
Scars improve gradually over several months, with the most noticeable improvement happening in the first month. In some cases, scar revision or resurfacing can further improve the appearance later on. Regular follow-up visits with your dermatologist are important after the procedure, both to monitor healing and to watch for any new skin cancers, since having one skin cancer increases your risk of developing another.