The Kennel Club in the United Kingdom and the American Kennel Club in the United States recognize only two varieties of Chihuahua: the long coat, and the smooth coat, also referred to as longhaired and shorthaired. The term smooth coat does not mean that the hair is necessarily smooth, as the hair can range from having a velvet touch to a whiskery feeling.
However, in May 2008, the Chihuahua Club of America voted that merles would not be disqualified in the United States, and would be fully registrable and able to compete in American Kennel Club (AKC) events.
Opponents of merle recognition suspect the coloration came about by modern crossbreeding with other dogs and not via natural genetic drift.
However, the British standard also states that a weight of 1.8–2.7 kg (4–6 lb) is preferred.
A clause stating that 'if two dogs are equally good in type, the more diminutive one is preferred' was removed in 2009.
It may take up to three or more years before a full longhaired coat develops.