Mohs Micrographic Surgery

Introduction

If you have been told you have a skin cancer and your dermatologist has mentioned Mohs micrographic surgery, this guide is written for you. Mohs surgery (named after Dr Frederic Mohs, who developed the technique) is a specialised way of removing certain skin cancers. Instead of removing the visible tumour and a large surrounding margin in one piece, the surgeon takes the cancer out in thin layers and checks each layer under a microscope right away. Removal stops only when no cancer cells are seen at the edges.

This approach is used most often for cancers on the face, ears, scalp, hands, feet, and genitals — areas where preserving normal skin matters for how you look and how the tissue works. It is also used for tumours that have come back after earlier treatment, have unclear borders, or are larger or more aggressive than usual.

This article explains what Mohs surgery is, who it is suited to, the alternatives, how to prepare, what happens on the day, how the wound is repaired, what recovery looks like, what risks exist, and what to expect in the months and years afterwards. The aim is to help you understand the procedure clearly so the conversation with your dermatologic surgeon feels familiar rather than overwhelming.

What Is Mohs Micrographic Surgery?

Mohs micrographic surgery is a tissue-sparing technique for removing skin cancer. It is performed by a dermatologic surgeon who has completed additional fellowship training in Mohs surgery. The same surgeon acts as both the surgeon and the pathologist on the day — they remove the tissue, prepare and examine the slides under a microscope, and decide whether another layer is needed.

The procedure differs from a standard surgical excision in two important ways:

• Margin checking is immediate. In a standard excision, the tumour and a surrounding rim of skin are removed in one piece, sent to a laboratory, and reported on days later. In Mohs surgery, the tissue is processed in a laboratory next to the operating room within an hour or two, and the result guides the next step in real time.
• Almost the full margin is examined. In a standard excision, the laboratory examines small vertical slices, which sample only a portion of the cut edge. In Mohs surgery, the tissue is cut and stained so that nearly the entire deep and peripheral margin is visible under the microscope. This is why Mohs surgery is associated with very high cure rates for the cancers it is used for.

Because of these advantages, the American Academy of Dermatology, the American College of Mohs Surgery, and other major dermatology bodies describe Mohs surgery as a preferred option for selected high-risk and cosmetically sensitive skin cancers. Whether it is the right choice in any individual case is a decision made with the treating dermatologist, based on the type of cancer, its location, its size, and prior treatment.

Why Is Mohs Surgery Performed?

Mohs surgery has two main goals: to remove the entire cancer with the highest possible certainty, and to take as little healthy skin as possible while doing so. These goals matter most when the cancer is in an area where every millimetre of skin counts — for example, near the eyelid, lip, or nostril — or where the cancer’s edges are difficult to see.

Doctors commonly use Mohs surgery for:

• Basal cell carcinoma (BCC) — the most common form of skin cancer. It rarely spreads to other parts of the body but can grow deeper and wider into local tissue if not fully removed.
• Squamous cell carcinoma (SCC) — the second most common form. Some types of SCC carry a higher risk of recurrence or spread, and Mohs surgery is often used in those cases.
• Selected rarer skin cancers such as dermatofibrosarcoma protuberans (DFSP), microcystic adnexal carcinoma, sebaceous carcinoma, and some early melanomas where Mohs or a related slow-Mohs technique may be considered.

The decision is also guided by published Appropriate Use Criteria (AUC) developed jointly by the American Academy of Dermatology, the American College of Mohs Surgery, and other societies. These criteria look at the tumour type, the location on the body, the size, and patient factors (such as previous radiation in the area, a weakened immune system, or aggressive features on biopsy) to decide when Mohs surgery is appropriate.

Who Is a Candidate?

Not every skin cancer needs Mohs surgery. Many small, low-risk basal cell carcinomas on the trunk or limbs are well treated by a simple excision, curettage and electrodesiccation, or other methods. Mohs surgery is generally considered when one or more of the following apply:

• The cancer is on the face, scalp, ears, eyelids, lips, nose, hands, feet, genitals, or shins — the so-called “H-zone” and other functionally or cosmetically sensitive areas.
• The borders of the tumour are unclear on examination — it fades into the surrounding skin rather than having a sharp edge.
• The cancer has come back after previous treatment (surgery, radiation, cryotherapy, or topical therapy).
• The biopsy shows an aggressive growth pattern, such as morpheaform (sclerosing) basal cell carcinoma, infiltrative basal cell carcinoma, or poorly differentiated squamous cell carcinoma.
• The tumour is large for its location.
• The patient is immunosuppressed (for example, after an organ transplant), where skin cancers can behave more aggressively.
• Tissue preservation is particularly important for function, such as around the eye, mouth, or fingertip.

When Mohs Surgery May Not Be the Right Choice

Mohs surgery may not be the preferred option when:

• The cancer is small, low-risk, and in an area where a simple excision gives excellent results.
• The cancer has already spread to lymph nodes or other organs — in that case, treatment focuses on systemic management as well as the skin.
• A patient cannot tolerate sitting through a procedure of several hours under local anaesthesia (for example, due to severe anxiety, certain movement disorders, or other medical reasons), although accommodations can often be made.

Suitability is decided after a clinical examination, review of the biopsy report, and a discussion of the alternatives.

Alternatives to Mohs Surgery

Several other treatments exist for non-melanoma skin cancer. The right choice depends on the type of cancer, its location, its size, and patient preferences. Common alternatives include:

Standard Surgical Excision

The surgeon removes the visible tumour along with a margin of normal-looking skin, then closes the wound. The tissue is sent to a pathology laboratory and reported on later. For low-risk tumours on the trunk or limbs, this method gives good cure rates and is simpler and shorter than Mohs surgery. If the report later shows cancer cells at the edge, a second procedure may be needed.

Curettage and Electrodesiccation

The tumour is scraped out with a sharp instrument (curette) and the base is treated with a small electric current. This is used for small, low-risk basal cell and squamous cell carcinomas on areas where scarring is less of a concern. It is not suitable for high-risk or facial tumours.

Cryotherapy

Liquid nitrogen is used to freeze and destroy the cancer. It is sometimes used for very superficial lesions or pre-cancerous spots, but is not the standard treatment for invasive skin cancers in sensitive areas.

Topical Therapies

Creams such as imiquimod or 5-fluorouracil are used for some superficial basal cell carcinomas and for actinic keratoses (pre-cancerous spots). They are not used for deep or high-risk cancers.

Radiotherapy

Radiation can be used as the primary treatment when surgery is not feasible — for example, in older patients, in areas that would be difficult to reconstruct, or when a patient cannot have surgery for medical reasons. It is also used after surgery in selected high-risk cases. Radiation is delivered over multiple sessions and has its own set of short- and long-term effects.

Systemic Therapy

For advanced basal cell carcinoma that cannot be treated with surgery or radiation, targeted drugs (hedgehog pathway inhibitors such as vismodegib and sonidegib) are options. For advanced squamous cell carcinoma, immunotherapy (such as cemiplimab) may be used. These are specialised treatments for selected patients and are not used for routine skin cancers.

Your dermatologist will explain which of these alternatives are reasonable for your specific cancer and why they may or may not recommend Mohs surgery as the preferred approach.

Preparing for Mohs Surgery

Mohs surgery is usually a planned, single-day procedure done under local anaesthetic. Preparation is straightforward, but a few steps make the day go more smoothly.

Before the Procedure

• Confirm the diagnosis and site. Bring your biopsy report and any photographs of the lesion. Skin cancer sites can be surprisingly hard to find once a biopsy has healed, so a clear photo or a marking placed by the referring dermatologist helps.
• Share your full medical history. Tell the surgical team about heart conditions, pacemakers or defibrillators (which can affect the use of electrocautery), diabetes, bleeding disorders, previous radiation to the area, and any history of poor wound healing.
• List your medications. Include prescription drugs, over-the-counter medicines, herbal supplements, and vitamins. Particular attention is paid to blood-thinning medication (such as aspirin, clopidogrel, warfarin, or direct oral anticoagulants) and supplements that can increase bleeding (such as fish oil, vitamin E, or ginkgo). Most blood thinners prescribed for a heart or stroke reason are continued through Mohs surgery, because the risk of stopping them is usually greater than the risk of bleeding. Your surgeon will give specific advice.
• Mention allergies. Especially to local anaesthetics, antibiotics, adhesive tape, or latex.

The Day Before and the Day of Surgery

• Eat a normal breakfast on the day of the procedure unless told otherwise. You are not having general anaesthesia, so fasting is not usually required.
• Wear loose, comfortable clothing. A button-up shirt is helpful if the surgery is on the face, neck, or upper chest.
• Avoid alcohol for at least 24 hours beforehand, as it can increase bleeding and bruising.
• Arrange a companion to drive you home, particularly if the surgery is on the face, near the eye, or if you may have a large bandage afterwards.
• Plan to spend most of the day at the clinic. The procedure itself is broken into stages with waiting time in between, so bring a book, headphones, or something to occupy you. Have a light snack with you.
• Clear your calendar for the rest of the day and ideally the following one or two days.

What Happens During Mohs Surgery

Mohs surgery is done in an outpatient setting. You stay awake throughout. Most of the visit is waiting; the actual surgical time is short.

Stage One: Marking and Anaesthesia

The surgeon examines the site, marks the area to be removed, and takes photographs for the medical record. A local anaesthetic, usually lidocaine mixed with adrenaline, is injected around the cancer. The injection stings briefly; after that, the area becomes numb and the rest of the procedure should not hurt.

Stage Two: Removing the First Layer

The surgeon removes the visible tumour together with a thin rim of surrounding tissue — usually only a few millimetres. The tissue is carefully oriented and marked so that the surgeon knows exactly which side faced which direction on your body. A pressure dressing is applied and you wait in a comfortable area while the tissue is processed.

Stage Three: Mapping and Microscopy

In the on-site laboratory, the tissue is frozen, sliced horizontally, mounted on glass slides, and stained. The surgeon examines almost the entire deep and peripheral edge under the microscope. A diagram (the “Mohs map”) is drawn so that any positive areas can be matched precisely back to your skin.

Processing usually takes between 45 minutes and an hour and a half.

Stage Four: Additional Layers if Needed

If the edges are clear, the cancer has been completely removed and the wound can be closed. If cancer cells remain in one or more areas, the surgeon returns, re-injects anaesthetic only where needed, and removes another thin layer of skin from those specific spots. The process repeats until the margins are clear.

Most cancers are cleared in one or two stages. A small number need three or more. Each stage adds time but typically not much additional pain, because the area stays numb.

Stage Five: Wound Repair

Once the cancer is completely removed, the surgeon discusses how to repair the wound. Options include:

• Side-to-side closure — the edges of the wound are brought together with stitches. This is the simplest option and works well for small wounds with enough nearby loose skin.
• Skin flap — nearby skin is moved into the wound while keeping its own blood supply. Flaps are designed to match colour and texture and to place scars along natural lines.
• Skin graft — a piece of skin is taken from another area (for example, in front of or behind the ear, the collarbone, or the inner upper arm) and placed over the wound.
• Healing by second intention — the wound is left open to heal on its own from the base upwards. This is sometimes the best choice in certain locations, such as the inner corner of the eye or parts of the ear, and it often gives surprisingly good cosmetic results.
• Repair by another specialist — in complex cases, particularly around the eyelid, lip, or nose, an oculoplastic or facial plastic surgeon may carry out the reconstruction, sometimes the same day and sometimes shortly afterwards.

The choice depends on the size and location of the wound, your skin’s elasticity and colour, and your preferences.

Recovery and Healing

Recovery from Mohs surgery is usually straightforward. The exact experience depends on the size and location of the wound and the type of repair done.

The First 24 to 48 Hours

• A pressure dressing is left in place to control bleeding and reduce swelling. Most surgeons ask you to keep it dry and untouched for the first day or two.
• Mild discomfort, throbbing, or a feeling of tightness is common as the anaesthetic wears off. Paracetamol (acetaminophen) is usually enough. Stronger painkillers are rarely needed.
• Swelling and bruising peak around 48 to 72 hours after surgery, especially around the eyes if the wound is on the forehead, nose, or cheek. Sleeping with the head slightly raised and applying a cool compress over the dressing can help.
• Some oozing is normal. Steady bleeding that soaks through the dressing should be controlled by firm pressure for 20 minutes; if it does not stop, contact the surgical team.

The First Two Weeks

• Wound care typically involves gentle cleaning, applying a layer of petrolatum-based ointment, and covering with a non-stick dressing. Antibiotic ointments are not always needed and may cause skin reactions in some people; follow the specific instructions you are given.
• Stitches are usually removed in 5 to 14 days, depending on the location. Stitches on the face come out earlier than those on the back or limbs.
• Avoid strenuous activity, heavy lifting, and bending for about a week, or longer for larger repairs. This reduces the risk of bleeding and wound separation.
• Avoid swimming pools, hot tubs, and saunas until the wound is fully closed.
• Smoking slows wound healing and increases the risk of complications, especially in skin flaps and grafts. Stopping — even temporarily — helps.

Scar Maturation

• Protect the scar from the sun with sunscreen (SPF 30 or higher) and a hat. New scars darken easily if exposed to sunlight.
• Gentle massage of the scar, once it is fully healed, may help it soften.
• Silicone gel or sheets are commonly used to improve scar appearance, particularly for raised or thickened scars.
• If a scar becomes thickened, lumpy, or restricts movement, treatments such as steroid injections, laser, or minor scar revision surgery are available later on.

Risks and Complications

Mohs surgery is considered very safe. Serious complications are uncommon. Still, every operation carries some risks, and it is reasonable to know what they are before consenting.

Common, Usually Minor

• Bleeding and bruising. Some bruising is expected, especially around the eyes for facial surgery.
• Swelling. Most marked in the first few days; resolves within 1 to 2 weeks.
• Pain and tightness. Usually mild and short-lived.
• Itching as the wound heals.

Less Common

• Infection. Reported in roughly 1 to 2 of every 100 cases. Signs include increasing pain, redness spreading beyond the wound, warmth, pus, or fever.
• Wound separation, particularly if the area is moved too soon or under tension.
• Delayed bleeding, sometimes a day or two after surgery, especially in patients on blood thinners.
• Altered sensation. Numbness, tingling, or rarely increased sensitivity near the scar. This often improves over months but may be permanent in a small area.
• Visible scarring. All surgery leaves a scar. The Mohs technique aims to minimise tissue loss, but the final scar size and shape depend on the original tumour size, the location, and how the wound is repaired.
• Skin flap or graft problems. Partial loss of a flap or graft can happen, particularly in smokers or in tissue with poor blood supply.

Rare

• Damage to small nerves or blood vessels near the surgical site. This can cause temporary weakness (for example, of a small facial muscle) or numbness; in rare cases, the change is long-lasting.
• Allergic reactions to local anaesthetic, antibiotics, or wound dressings.
• Significant cosmetic concerns that require additional reconstructive procedures.

Your surgical team will discuss the specific risks for your tumour and location before you sign the consent form.

Life After Mohs Surgery

For most people, the Mohs procedure itself is one day in a longer story of skin health. After the wound has healed, attention shifts to two things: watching for recurrence at the original site, and screening for new skin cancers elsewhere.

Cure Rates and Recurrence

Across published studies, Mohs surgery achieves cure rates of around 97 to 99 per cent for previously untreated basal cell carcinomas and around 94 to 97 per cent for previously untreated squamous cell carcinomas, depending on tumour features. Cure rates for tumours that have recurred after earlier treatment are also higher with Mohs surgery than with most other methods, although a little lower than for primary tumours.

Recurrences, when they happen, most often appear within the first five years — though late recurrences are possible. This is why regular skin checks are important even after a successful procedure.

Follow-up Schedule

There is no single fixed schedule, but a common pattern is:

• A wound-check visit within one to two weeks for suture removal, if needed.
• A clinical review at around six to eight weeks to assess healing and the scar.
• Full skin examinations every 6 to 12 months for several years afterwards.

People who have had one non-melanoma skin cancer are at increased risk of having another. Major dermatology societies recommend regular full-skin examinations and prompt review of any new, changing, or non-healing skin lesion.

Sun Protection and Skin Care

The single most useful long-term change for most patients is consistent sun protection. This typically includes:

• Daily broad-spectrum sunscreen (SPF 30 or higher) on exposed skin.
• Wide-brimmed hats and protective clothing during outdoor activities.
• Avoiding the strongest midday sun and indoor tanning beds.
• Self-examinations of the skin every one to two months, looking for new or changing spots, and reporting them to your dermatologist.

For patients with many sun-damaged areas or pre-cancerous spots (actinic keratoses), the dermatologist may also recommend periodic treatment of those areas with topical creams, photodynamic therapy, or cryotherapy.

Emotional Adjustment

A skin cancer diagnosis and a scar on a visible area can take some emotional adjustment. Most people find that the scar settles and becomes far less noticeable over the following months. If the scar bothers you significantly — physically or emotionally — talk to your dermatologic surgeon about options for scar improvement. Speaking to a counsellor or a support group can also help, particularly for those who have had multiple skin cancers.

Choosing a Surgeon and a Centre

Mohs surgery requires both a surgeon trained in the technique and an on-site laboratory able to process and stain tissue accurately within an hour or two. When considering where to have the procedure, useful things to ask about include:

• The surgeon’s qualifications in dermatology and additional training or fellowship in Mohs surgery.
• Experience with the specific type and location of your cancer.
• Whether the laboratory is on-site and integrated with the surgical workflow.
• The team’s approach to reconstruction, including whether complex repairs are done in-house or with a plastic surgery or oculoplastic colleague.
• How follow-up is organised after the procedure.
• Clear communication and a sense of rapport with the surgeon and team.

It is reasonable to meet more than one surgeon before deciding, particularly for complex cases.

Frequently Asked Questions

Will I be awake during Mohs surgery?

Yes. Mohs surgery is done under local anaesthetic, which numbs only the area being treated. You stay awake, can talk to the team, and can move freely during waiting periods. General anaesthetic is rarely used for Mohs surgery, although sedation is sometimes considered for very anxious patients or for complex reconstructions.

How long will the whole day take?

Most patients spend between four and eight hours at the clinic, although the actual time the surgeon is operating is much shorter. Most of the day is spent waiting while tissue is processed and examined. The total time depends on how many stages are needed and what type of repair is done.

Will it hurt?

The injection of local anaesthetic stings briefly, much like a dental injection. After that, the surgical area is numb and you should feel pressure or tugging but no sharp pain. If the area starts to wake up between stages, more anaesthetic can be added easily. Pain afterwards is usually mild and well controlled with paracetamol.

How big will the scar be?

The scar depends on the size of the tumour after complete removal and the type of repair. Mohs surgery aims to remove only as much skin as needed to clear the cancer, which often means a smaller defect than a standard excision would create. However, the original visible tumour may extend further under the skin than it appears on the surface, so the final wound can be larger than the spot you came in with.

Will the cancer come back?

Most cancers treated with Mohs surgery do not return at the same site. Long-term cure rates are around 97 to 99 per cent for primary basal cell carcinomas. Recurrences are more common when the original tumour was large, aggressive, or had been treated before. Regular follow-up checks help catch any recurrence or new cancer early.

Can the same cancer come back somewhere else?

Basal cell and squamous cell carcinomas can recur at the original site, but they can also appear as new tumours elsewhere on sun-damaged skin. People who have had one skin cancer are at higher risk of developing another, which is why long-term skin surveillance is important.

Is Mohs surgery used for melanoma?

For most invasive melanomas, wide local excision (with margins determined by the depth of the tumour) is the standard approach, sometimes combined with sentinel lymph node biopsy. For certain melanomas on the face — particularly lentigo maligna and lentigo maligna melanoma — some centres use Mohs surgery or a related “slow Mohs” technique with specialised staining. Whether this is suitable depends on the type of melanoma and the centre’s practice.

Can Mohs surgery be done on children?

Skin cancers requiring Mohs surgery are uncommon in children but can occur, particularly in children with conditions that increase skin cancer risk (such as xeroderma pigmentosum or basal cell naevus syndrome). When Mohs surgery is needed in a child, sedation or general anaesthesia is often used and the procedure is planned with a paediatric team.

What if the cancer is bigger than expected?

One of the strengths of Mohs surgery is that it adapts to what is found. If the tumour extends further than expected, more layers are removed until the edges are clear. If the resulting wound is large, the surgeon may close it the same day, leave it to heal naturally, or plan a staged reconstruction with another specialist. You will be involved in this decision before the wound is closed.

Can I drive home afterwards?

For small wounds in areas that do not affect vision, some people drive themselves home. For surgery on or near the eye, for larger wounds, or if you have had any sedative medication, you should arrange a lift. Many centres ask all patients to arrange a companion, just in case.

When can I return to work?

Many people return to office-based or light work the next day, especially after a small procedure on the trunk or limbs. Visible facial wounds and physically demanding jobs usually mean a few days to a week off. Heavy lifting, contact sports, and strenuous exercise are typically avoided for one to two weeks. Your surgeon will give specific advice based on your wound and your work.

Conclusion

Mohs micrographic surgery is a precise, layer-by-layer technique for removing certain skin cancers, used most often when accuracy and tissue preservation matter most — on the face, around the eyes and lips, on the ears, hands, and other sensitive areas, and for tumours that have come back or have unclear edges. By examining nearly the entire margin of the removed tissue under the microscope during the procedure, the surgeon can confirm complete removal before closing the wound.

For the cancers it is used for, Mohs surgery is associated with high cure rates and good preservation of normal skin and function. It is not the right approach for every skin cancer, and several other effective treatments exist for lower-risk tumours. The decision rests with you and your dermatologic surgeon, after looking at the type of cancer, where it is, how it has behaved, and what reconstruction will be involved.

Whatever the result on the day, the long-term picture is shaped just as much by what comes next: careful wound care, regular skin checks, sun protection, and prompt attention to any new or changing spot. With those in place, most people who have had Mohs surgery go on to many cancer-free years afterwards.