context: Keratoacanthoma is a dome-shaped lump or tumor that grows on your skin. Once you spot it, it's important to talk to your doctor. It sometimes happens to people before they get squamous cell carcinoma, the second most common type of skin cancer. If you catch the problem early, treatment usually works well. You might think you have a pimple or boil at first, but keratoacanthoma can grow fast and get as big as a quarter in a couple of months. It looks like a small, red or skin-colored volcano -- there's a distinctive crater at the top of the lump that often has keratin, or dead skin cells, inside. You'll usually see keratoacanthoma on skin that's been exposed to the sun, like your head, neck, arms, the backs of your hands, and sometimes your legs. It often starts in a hair follicle. Men are twice as likely to have the condition as women. It's also more common for white people than those with darker skin and in people age 60 and over. It's rare for anyone under age 20 to have keratoacanthoma. Doctors don't know what causes keratoacanthoma, but some things make you more likely to get it: Sun exposure HPV infection Some cancer-causing chemicals Your genes A weak immune system Your doctor will probably take a biopsy, or a piece of the tumor, to send to an expert called a pathologist, who will examine the sample under a microscope. The cells of keratoacanthoma often look just like those of squamous cell carcinoma. Your doctor will have to remove a large-enough piece so the pathologist can see the shape of the tumor with its distinctive crater. The most common treatment is surgery to remove the keratoacanthoma. You can have the procedure in your doctor's office with medicine to numb the area around the tumor. There are a few different surgeries your doctor may use. He can: Scrape off the tumor and seal up the wound. Apply liquid nitrogen to freeze and destroy the tumor. This is called cryosurgery. Cut the tumor out and use stitches to close the area. Remove one layer of tissue at a time and examine each one under a microscope to make sure all abnormal cells are gone. This is called Mohs surgery. It's the most precise way to get rid of keratoacanthoma but also the most expensive. If you can't have surgery, or if you have multiple keratoacanthomas, you can try other treatments: The chemotherapy drug 5-fluorouracil. You can get it as a cream to rub on your skin or as a shot. Injections of the chemotherapy drugs bleomycin or methotrexate Radiation Drugs like retinoids that you take by mouth It's not unusual for a single keratoacanthoma to shrink and disappear on its own after several months. But it may leave a worse scar than one from surgery. It could also come back, so it's best to get it removed. If you don't treat it, keratoacanthoma can spread throughout your body. Once you've had one keratoacanthoma, you may be more likely to get others in the future. Check your skin regularly for any lumps or unusual spots, and see your doctor for a full-body exam twice a year. It's also important to protect your skin from sun damage. Avoid going outside from 10 a.m. to 4 p.m., when the sun is strongest. Use a broad-spectrum sunscreen with SPF of 15 or higher. Wear sun-protective clothing and hats when you're outside. Don't use tanning beds. These conditions are extremely rare, but they can cause multiple keratoacanthomas to grow on your skin. There can be so many that doctors can't remove them all with surgery. Ferguson- Smith. This can cause as many as 100 keratoacanthomas at one time. It's the most common type of multiple keratoacanthoma. It's a condition you can get through your genes and may start as early as age 8. You may take retinoid medicine to try to reduce the number of additional tumors. Grzybowski syndrome is even more rare. It causes tumors that are smaller but itch intensely. They may even show up in the mouth.