Standards
Breed standards for this dog do not generally specify a height, only a weight and a description of their overall proportions. As a result, height varies more than within many other breeds. Generally, the height ranges between 6 and 10 inches (15 to 25 cm) at the withers. However, some dogs grow as tall as 12 to 15 inches (30 to 38 cm). AKC show dogs (American standard) must weigh no more than 6.0 lb (2.7 kg). The Fédération Cynologique Internationale (FCI) standard calls for dogs ideally between 1.5 and 3.0 kg (3.3 to 6.6 lb), although smaller ones are acceptable in the show ring. However, pet-quality Chihuahuas (that is, those bred or purchased as companions rather than show dogs) can, and do, range above these weights, to 10 pounds (4.5 kg), or even more if they have large bone structures or are allowed to become overweight. This does not mean, however, that they are not purebred Chihuahuas, it only means that they do not meet the requirements to enter a conformation show. Oversize Chihuahuas are seen in some of the best, and worst, bloodlines.
Coat
The AKC (American Kennel Club) recognizes two varieties of Chihuahua: the long-coat and the smooth-coat, also referred to as short-haired. They are genetically the same breed, and are often present in the same litter, though in many kennel clubs, including the AKC, they are judged in separate categories. 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. Long-haired Chihuahuas are actually smoother to the touch, having soft, fine guard hairs and a downy undercoat, which gives them their fluffy appearance. Unlike many long-haired breeds, long-haired Chihuahuas require no trimming and minimal grooming. Contrary to popular belief, they also typically shed less than their short-haired counterparts. It may take up to two or more years before a full long-haired coat develops
This breed requires expert veterinary attention in areas such as birthing and dental care. Chihuahuas are also prone to some genetic anomalies, often neurological ones, such as epilepsy and seizure disorders.Chihuahuas, and other toy breeds, are also prone to the sometimes painful disease Hydrocephalus. It is often diagnosed by the puppy having an abnormally large head during the first several months of life, but other symptoms are more noticeable (since "a large head" is such a broad description). Chihuahua puppies exhibiting Hydrocephalus usually have patchy skull platelets rather than a solid bone, and typically are lethargic and do not grow at the same pace as their siblings. A true case of Hydrocephalus can be diagnosed by a veterinarian, though the prognosis is grim.Chihuahuas are also known for their moleras, a soft spot in their skulls. Chihuahuas are the only breed of dog to be born with an incomplete skull. The molera does fill in with age, but great care needs to be taken during the first six months until the skull is fully formed. Many veterinarians are not familiar with Chihuahuas as a breed, and mistakenly confuse a molera with hydrocephalus. The Chihuahua Club of America has issued a statement regarding this often deadly misdiagnosis.Chihuahuas can also be at risk for hypoglycemia, or low blood sugar. Left unattended, hypoglycemia can lead to coma. Chihuahuas are also prone to eye infections due to their large, round, protruding eyes and their relatively low ground clearance. Chihuahuas also have a tendency to tremble but this is not a health issue, rather it takes place when the dog is stressed or excited. One reason for this may be because small dogs have a higher metabolism than larger dogs and therefore dissipate heat faster. Although figures often vary, as with any breed, the average lifespan for a Chihuahua is approximately 8 to 18 years of age.Chihuahuas are sometimes picky eaters, and care must be taken to provide them with adequate nutrition. At the same time, care must be exercised not to overfeed this tiny breed. Overweight Chihuahuas are prone to joint injuries, tracheal collapse, chronic bronchitis, and shortened life span.