Mohs surgery for skin cancer: what happens, risks and recovery

The surgeon removes the visible cancer and a thin layer around it, then maps the tissue and examines the edges under a microscope while you wait. If cancer cells are seen at the edge, only that area is taken further, and the process is repeated. The aim, described by the British Association of Dermatologists, is to remove the cancer with as much certainty as possible while keeping healthy skin.

This makes it attractive where every millimetre counts. The British Association of Dermatologists and Skin Health Info list the situations in which it is recommended: basal or squamous cell cancers, particularly on the head and neck, with unclear edges, in sensitive places such as eyelids, nose, ears and lips, that are large, or that have come back after earlier treatment.

The technique is named after Dr Frederic Mohs, who developed it in the 1930s, according to Skin Health Info. Where the repair is complicated, the British Association of Dermatologists lists referral to a specialist surgeon as one of the closure options.

Many skin cancers are treated well by a standard excision, and not every cancer needs Mohs surgery. The British Association of Dermatologists lists observation, conventional surgical excision and non-surgical treatments such as radiotherapy as alternatives. The right choice depends on the type of cancer, its size, how clearly the edges can be seen and where it is.

If you are unsure why Mohs has or has not been advised for you, ask the dermatologist to explain the reasoning.

The British Association of Dermatologists says you should eat and drink normally unless told otherwise, bring comfortable clothes and a list of medicines, and arrange transport because driving afterwards is inadvisable. Tell the team about blood-thinning medicines, because bruising and bleeding are more likely with them.

Skin Health Info suggests stopping smoking for two weeks before and after surgery, which supports healing. Bring something to read or occupy you, as there are waiting periods between stages while the slides are prepared and examined.

The surgeon marks the cancer and numbs the area with local anaesthetic. After the first layer is removed, the wound is dressed and you wait, often in a waiting room, while the tissue is processed and read. Skin Health Info says the average procedure time is around three hours, and the British Association of Dermatologists says up to three hours, with extra anaesthetic given between stages as needed.

The British Association of Dermatologists says that in 90% of cases the cancer is cleared after one or two stages, though some people need more. When the margins are clear, the repair is planned. The options are letting the wound heal by itself, stitching, a skin graft, a skin flap or referral to a reconstructive surgeon, depending on the site, the size and your preferences.

Bleeding and bruising are the most common problems, and more likely if you take blood-thinning medicines. Pain is usually controlled with over-the-counter painkillers, and every skin operation leaves a scar. Infection is uncommon and may need antibiotics. Nerve damage causing numbness is uncommon, and recurrence of the cancer is described as very rare, though you should be told how that applies to your own cancer.

The repair can be as important as the cancer removal, particularly near the eye, nose or lip, where function matters. It is reasonable to ask who will do the repair, how many stages might be needed, and what the likely scar will look like before agreeing to go ahead.

Keep dressings dry for at least 48 hours, as the British Association of Dermatologists advises, and take painkillers as needed. Skin Health Info advises avoiding driving for several days. Return to work when comfortable, which the British Association of Dermatologists puts at one to two weeks after a major reconstruction. A staged picture is in the recovery timeline for this operation.

Spreading redness, increasing pain, heat, discharge or fever in the first days suggest infection, and the dermatology unit or GP should be contacted promptly. If bleeding does not stop with firm pressure for ten to fifteen minutes, seek urgent help at an emergency department, or call 999 if it is heavy.