The Chihuahua (/tʃɪˈwɑːwə, -wɑː, -ˈwaʊ.ə/ (listen); Spanish: chihuahueño) is the smallest breed of dog, and is named after the Mexican state of Chihuahua. Colonial records refer to small, nearly hairless dogs at the beginning of the 19th century, one of which claims 16th-century Conquistadores found them plentiful in the region later known as Chihuahua. Small dogs such as Chihuahuas were also used as living heating pads during illness or injury. Chihuahuas as we know them today remained a rarity until the early 20th century; the American Kennel Club (AKC) did not register a Chihuahua until 1904. Chihuahuas can be easily frightened or provoked to attack, so are generally unsuitable for homes with small children. The breed tends to be fiercely loyal to one particular person and in some cases may become overprotective of the person, especially around other people or animals, and tend to have a 'clannish' nature, often preferring the companionship of other Chihuahuas or Chihuahua mixes over other dogs.