Kegel: An exercise that helps prevent and treat incontinence by strengthening pelvic floor muscles.

keloid: An unusually hard or thick scar that forms after surgery or an injury.

keratectomy: A procedure in which a laser is used to correct vision problems by reshaping the cornea.

keratin: A protein and the major component of the cuticle and cortex layers of hair; the same protein is found in nails, feathers, claws, and hooves.

keratinocytes: Cells of the epidermis that produce a tough protein called keratin and form a soft, protective sheet for the body.

keratoconjunctivitis sicca: Persistent dryness of the eye.

keratoderma blennorrhagica: A skin rash that sometimes occurs along with an autoimmune condition called Reiter's syndrome.

Keshan disease: Heart disease caused by a lack of selenium, an element that the body needs to function properly.

ketones: Substances produced when the body burns fat for energy or when the body doesn't have enough insulin.

kidney failure: The final stage of chronic kidney disease. At this point, the kidneys can no longer eliminate waste products from the body.

kyphoplasty: A surgical procedure that eases or eliminates the pain of spinal fractures. It also restores vertebrae that have collapsed due to fractures to their normal size.