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What is Mohs Surgery?

Microscopically controlled surgery was developed by Dr. Frederick Mohs in the 1940s as a more precise way to remove skin cancers. Originally, chemicals were applied to the skin and the entire surgical procedure took several days. The technique has been refined over the years to the point where the skin cancer is now removed and examined under the microscope for any remaining tumor almost immediately. The basic principle behind the Mohs technique is to remove the entire skin cancer without taking any more normal skin than is absolutely necessary.

Often times what can be seen on the skin surface only represents a part of the actual skin cancer, "the tip of the iceberg" so to speak. With our eyes alone, we cannot see the "roots" of the skin cancer that are under the skin surface. Instead of guessing approximately how far these "roots" extend under and around the skin cancer, the microscope is used to trace out and map the exact extent of the tumor. The surgeon may then remove only the cancerous tissue. This prevents either removing too little or leaving the tumor behind to come back, or recur (usually larger) in the future, or from removing too much and creating a larger than necessary wound. In essence the best of both worlds is achieved. The entire skin cancer is removed and as much as possible of the normal skin is preserved. The Mohs microscopically controlled technique offers a cure rate of 98-99%, the highest of any technique available.

Since Mohs surgery requires highly-trained personnel and can be time consuming, it is reserved only for certain cases. The four most common indications for using the Mohs technique are:

  • The tumor is located on a structure that is so important that one wishes to remove only the diseased tissue and preserve as much of the normal skin as possible (face, hand, etc...)

  • The cancer has been previously treated and has come back (recurred)

  • The margin or extent of the tumor cannot be discerned

  • The tumor occurs in an area of the body where it is not effectively curable with other methods

The video below is from the American College of Mohs Surgery and covers all the basics of skin cancer and the details of the Mohs Surgery process.


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There is usually no special preparation required before Mohs surgery. We recommend being well rested having a good breakfast on the morning of surgery. Unless it is medically necessary, we ask that you do not take aspirin, aspirin-containing products, such as Anacin and Bufferin;"vitamin E, vitamin C or other supplements for fourteen days prior to surgery unless a physician has prescribed them for you. Ibuprofen or naprosyn containing products, such as Motrin;" Advil or Aleve should also be avoided for fourteen days prior to surgery. You may take acetaminophen products, such as Tylenol:" Take all of your other usual medications unless directed otherwise. We also require that you do not drink any alcohol for seven days prior to surgery, since this will cause more bleeding. Smoking also has a negative impact on the healing process and should be stopped one day prior to surgery and for one week after surgery. You are encouraged to contact your primary care physician for assistance with smoking cessation.

We recommend washing your hair the night before or the morning of surgery, as your wound and initial dressing must remain dry for the first 48 hours as directed by your surgeon. We also suggest you wear loose fitting, comfortable clothing.

The length of the surgery varies greatly depending on the size and location of the skin cancer. You should plan on spending most of the day with us. You should also arrange to have someone drive you home after your surgery.

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Again, eat a good breakfast, take your normal medications unless directed otherwise, wear comfortable clothing and be prepared to spend the entire day. Mohs surgery is a minor surgical procedure, performed on an outpatient basis in an ambulatory surgery or office setting. You should arrive for your appointment 15-30 minutes early  in order to complete any registration and check in requirements. You will be escorted to a consultation room where you will be asked a few routine, pre-operative questions and have all your questions answered.  Once your questions  are answered, your consent for the surgery will be obtained.

Once in the room, a local anesthetic (usually lidocaine) will be injected to the area. This is generally the only part of the surgery that causes any discomfort and it is usually no worse than what was done when the lesion was biopsied. Once the area is numb, a small layer of tissue will be removed and a map of it will be made. The small amount of bleeding that may occur will be stopped with a cautery unit and a dressing will be placed on your wound. The tissue will then be processed.

During this time, the tissue will be frozen, stained and cut for microscopic slides. Your doctor will then review these slides under the microscope and create a map of any tumor remaining. In this manner, the exact location of any residual tumor may be determined and then removed, without having to remove any of the skin that appeared normal under the microscope.

Although the area should still be numb from the first stage, a little more anesthetic agent is added to keep the area numb for further stages and the reconstruction. Using the microscopic "map" of the skin cancer, only the area or areas seen as cancerous are then removed. The process is repeated until the entire skin cancer is removed. It is this process of systematically searching out and removing all of the "roots" of the skin cancer that gives Mohs surgery its cure rate of 98-99%.

Although some skin cancers are removed in one stage, the average tumor requires two or three stages for removal and some require several more. If your skin cancer should require more than one stage, try not to get discouraged. The intent is to remove the entire skin cancer and to preserve any uninvolved normal skin. To achieve these goals, the tissue must be removed in very small, conservative layers.

When the tumor has been completely removed, a decision will be made with you as to the best method to repair the wound. Depending on the size and location of the wound, it may be allowed to heal by itself, dosed side to side with sutures, or dosed using a local flap or graft. Although most wounds are repaired in our surgical suite on the day of surgery, it is occasionally necessary to utilize the unique skills of other surgical specialists. In these cases, the reconstruction will be arranged to occur on a subsequent day shortly thereafter.

  • Eat a good breakfast

  • Bring something to do (Book, iPod, DVD player, etc.)

  • Take your normal medication

  • Bring a snack/lunch (refrigerator available)

  • Wear comfortable clothing

  • Arrive 15 – 30 minutes early

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Detailed written instructions on wound care will be given to you and reviewed upon completion of the surgery. Essentially, you will leave the original bandage on for the first 48 hours and then you will dean the wound twice a day, place an ointment (white petrolatum I Polysporin Ointment) on the wound and then cover it with a small dressing. This will be continued until the sutures are removed (usually 7 to 14 days after the surgery or until after they dissolve). It is very important to keep the wound moist with ointment and not to let it dry out. When a wound dries and a scab forms, it will take longer to heal and is more likely to form a more noticeable scar.

Most patients report minimal amount of discomfort the first day or two following surgery. This discomfort usually responds readily to Tylenol™ Extra Strength in its usual dosage. We do not want you to take any aspirin, naprosyn or ibuprofen containing products for three days following surgery. There may also be a normal sensation of itching or tightness that is experienced in the immediate post-operative period. Some minimal spot bleeding is normal and expected post-surgery.

Often times patients will have "black and blue" marks and swelling around the surgery site. This reaction is particularly frequent and exuberant around the eyes. Most of this is your body's reaction to being wounded. Cells from other areas come to the wound to help repair it. In doing so, they create swelling. This usually gets worse for the first three days after surgery and then slowly begins to improve.

You may also experience some numbness around the area that was operated on. There are many small nerves that carry sensation to the skin. Some of these may be cut during surgery and it may take 6-12 months before full sensation returns. Rarely the skin cancer involves larger nerves. When these are cut, the loss of sensation or muscle weakness may be permanent.

Remember, every surgical procedure produces some form of a scar. Although every attempt will be made to minimize and hide the scar, the extent of the scarring depends on the location, size and depth of the skin cancer and the healing properties of the individual. The scar will continue to improve for 8-18 months. After the first three months the area can be gently massaged, as directed by your dermatologist, if it feels thick or lumpy.

You may be seen for suture removal seven to fourteen days after surgery and in many cases a few months after surgery to make sure everything is healing appropriately. After the three month visit, you should be monitored every six months to a year for new skin cancers. Although the chance of having the skin cancer recur after Mohs surgery is only 1-2o/o, it does happen and the area should be monitored. Even more importantly, there is a good possibility that a new skin cancer may develop in other areas in the future. Remember that 50% of patients will have a second skin cancer within five years of their first. This is why it is very important to protect yourself from the sun's rays and to have a dermatologist follow your skin closely. If you should notice any new lesions and suspect they might be skin cancers, you should schedule an appointment promptly and not wait the six or twelve months before the next scheduled visit.

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Click below watch the Mohs patient education video created by the American College of Mohs Surgery. Lasting 9 minutes and 20 seconds, this video provides a thorough overview of Mohs Surgery for skin cancer treatment. 

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