Merck Manual

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Gregory L. Wells

, MD, Ada West Dermatology, St. Luke’s Boise Medical Center, and St. Alphonsus Regional Medical Center

Last full review/revision May 2019| Content last modified May 2019
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Keratoacanthomas are round, firm, usually pink or flesh-colored growths that have a central crater that is scaly or crusted. Some keratoacanthomas may be a form of squamous cell carcinoma.

Keratoacanthomas appear most commonly on sun-exposed areas, the face, forearms, and back of the hands and grow quickly. In 1 or 2 months, they typically grow into lumps about 1 inch (about 2.5 centimeters) wide, but sometimes they grow over twice as large. They may spontaneously disappear within a few months, often leaving a scar.

The cause of keratoacanthomas is unknown. Most doctors consider keratoacanthomas to be a form of squamous cell carcinoma, a type of skin cancer.


  • Biopsy

Because a keratoacanthoma might be cancerous, doctors often do a biopsy, in which a piece of skin is removed and examined under a microscope. Sometimes they completely remove the tumor during the biopsy.


Because keratoacanthomas can be caused by exposure to sun, people can help prevent this cancer by doing the following:

  • Avoiding the sun: For example, seeking shade, minimizing outdoor activities between 10 AM and 4 PM (when the sun’s rays are strongest), and avoiding sunbathing and the use of tanning beds

  • Wearing protective clothing: For example, long-sleeved shirts, pants, and broad-brimmed hats

  • Using sunscreen: At least sun protection factor (SPF) 30 with UVA and UVB protection used as directed and reapplied every 2 hours and after swimming or sweating but not used to prolong sun exposure


  • Surgery or injections of methotrexate or 5-fluorouracil

There is no guarantee that a keratoacanthoma will spontaneously disappear, and even when they do disappear, there is often a scar. Thus, keratoacanthomas are usually cut out or scraped (curetted) or injected with methotrexate or 5-fluorouracil.

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