Guinea pigs are generally hardy, healthy animals but are susceptible to certain diseases. They cannot make their own vitamin C and require supplementation or they may develop scurvy. Guinea pigs get various tumors, particularly skin and mammary tumors. Guinea pigs also get abscesses (accumulations of pus and bacteria) in lymph nodes, skin, muscles, teeth, bones, and internal organs. They are very prone to development of urinary calculi that form in the bladder, kidneys, or ureters which may become lodged, causing a life-threatening obstruction. In addition, guinea pigs often are affected by ringworm and can get fleas and lice. Barbering is a problem, usually associated with boredom, in which the guinea pig chews or barbers its own hair or the hair of its cage-mate. Pododermatitis, or bumblefoot, in which sores develop on the bottom of the feet from pressure, is common in overweight animals housed on wire-bottomed or dirty cages that abrade the feet.