Because calluses form in response to repeated friction or irritation, most occur on the bottom of the feet. However, many people have calluses on the middle finger of their dominant hand as a result of the friction caused by handwriting with a pencil or pen. Musicians, weightlifters, gardeners, chefs, and other professionals who repeatedly use instruments or tools often have calloused hands because of the nature of their work. While most calluses are not harmful and can be dissolved, sanded, or filed without pain, some forms of calluses can be problematic. For example, a corn is a funnel-shaped callus that forms on thin surfaces (most commonly on the top of the toes or fingers). Because of its shape (specifically, its pointed bottom), corns can cause tissue damage and ulceration. Calluses can be prevented by minimizing rubbing and pressure by wearing properly fitting footwear and protective pads. Existing calluses may go away once the irritation is removed. However, some require paring down by a podiatrist. Individuals with diabetes or poor blood circulation should be extra careful in preventing the formation of calluses and treating existing ones, because of a higher risk of complications. If a corn or callus becomes swollen or painful, medical attention may be necessary.