The Chihuahua is a toy dog from Mexico, named after the Mexican state of Chihuahua. The FCI calls it “regarded as the smallest pedigree dog in the world”.[1] It comes in two coat types, smooth and long, and in almost every colour.[1]
The breed standard
The FCI standard sets only a weight: 1–3 kg, with 1.5–2.5 kg ideal. Height is not considered. The head is apple-shaped, the ears are large and upright, and the tail is carried high. All colours are allowed except merle, and a dog with an open fontanelle (a soft spot on the skull) is disqualified.[1] The American Kennel Club gives a height of 5–8 inches and a weight of up to 6 pounds (2.7 kg).[2] These are show-ring ideals, not averages. The median adult Chihuahua in a study of UK veterinary records weighed 3.4 kg.[3]
Name and origin
The FCI says the breed carries the name of the Mexican state. Its standard assumes that the dogs were captured and domesticated by native peoples in Toltec times, and links them to statues of a toy dog called the “Techichi”.[1] That descent has not been shown. One DNA study found a maternal-line DNA type shared with an ancient Mexican dog in 5 of 14 Chihuahuas tested.[4] A later study of dogs in the Americas found that almost all pre-contact dogs disappeared after Europeans arrived. Only two of 169 modern American dogs carried their maternal-line DNA, a Chihuahua and a mixed-breed dog from Nicaragua.[5] A study of breed relationships places the Chihuahua in a toy-dog group with the Chinese Crested, and the authors write that both are believed to have originated in Central America.[6] The AKC recognised the Chihuahua in 1904.[7]
Health and lifespan
UK veterinary records show a wide spread of lifespans. Life expectancy at birth was 7.9 years, but the age at which remaining life expectancy fell to 1.5 years was 15–16, the latest of 18 breeds.[8] A study of Chihuahuas under UK veterinary care in 2016 found periodontal disease in 13.5%, obesity in 5.9%, retained baby teeth in 5.7% and patellar luxation (a slipping kneecap) in 4.0%. Heart disease was the commonest cause of death, at 18.8%.[3] Chihuahuas were about six times as likely as crossbred dogs to have patellar luxation.[9] In Sweden, 38% of 97 apparently healthy Chihuahuas had mitral valve leakage, though the dogs came through the breed club.[10] In one study of client-owned Chihuahuas, 46 of 50 had at least one persistent fontanelle, but the dogs were not a random sample.[11]
Behavior
In an owner-reported survey of 56 Chihuahuas, 16.1% were reported to have snapped, bitten or tried to bite an unfamiliar person in the recent past, 5.4% a member of the household and 17.9% an unfamiliar dog. The averages across the 33 breeds in the survey were 4.7%, 2.0% and 10.7%. The authors name Chihuahuas among the breeds that scored higher than average for aggression towards both people and dogs.[12] Breed explains only about 9% of behavioural differences between individual dogs, so an individual’s behaviour can differ a lot from the breed’s average.[13]
Records and popularity
As listed by Guinness World Records, the shortest dog living is Pearl, a Chihuahua measured at 9.14 cm tall in 2022. The previous holder, Miracle Milly, a Chihuahua, measured 9.65 cm in 2013.[14] The Chihuahua ranked 24th on the AKC’s list of most popular breeds in 2025.[15] In UK veterinary records, Chihuahuas made up 3.46% of dogs in 2016, and their share of new dogs rose from 1.01% in 2005 to 5.35% in 2016.[3]
Sources
- FCI breed standard 218, Chihuahua
- American Kennel Club, Chihuahua breed page
- O’Neill et al. 2020, BMC Veterinary Research 16: 52 (Chihuahuas under UK veterinary care)
- van Asch et al. 2013, Proceedings of the Royal Society B 280: 20131142 (mitochondrial DNA of American breeds)
- Leathlobhair et al. 2018, Science 361: 81–85 (dogs in the Americas)
- Parker et al. 2017, Cell Reports 19: 697–708
- American Kennel Club, breeds by year recognized
- Teng et al. 2022, Scientific Reports 12 (life tables by breed)
- O’Neill et al. 2016, Canine Genetics and Epidemiology 3: 4 (patellar luxation)
- Pålsson, Vestberg & Tidholm 2025, Journal of Veterinary Cardiology (mitral regurgitation in Chihuahuas)
- Kiviranta et al. 2021, Journal of Veterinary Internal Medicine (fontanelles in Chihuahuas)
- Duffy, Hsu & Serpell 2008, Applied Animal Behaviour Science 114: 441–460
- Morrill et al. 2022, Science 376 (breed and behaviour)
- Guinness World Records, shortest dog living (height)
- American Kennel Club, most popular dog breeds of 2025