A Cornish Rex is a breed of domestic cat. The Cornish Rex has no hair except for down. Most breeds of cat have three different types of hair in their coats: the outer fur or "guard hairs", a middle layer called the "awn hair"; and the down hair or undercoat, which is very fine and about 1 cm long. Cornish Rexes only have the undercoat. Cornish Rex are prone to hair loss and many will develop a very thin coat or even go bald over large parts of their body. The curl in Cornish Rex fur is caused by a different mutation and gene than that of the Devon Rex. The breed originated in Cornwall, Great Britain.