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 six and ten inches. However, some dogs grow as tall as 12 to 15 inches (30 to 38 cm). Both British and American breed standards state that a Chihuahua must not weigh more than six pounds for conformation. However, the British standard also states that a weight of two to four pounds is preferred and that if two dogs are equally good in type, the more diminutive or smaller is preferred. The Fédération Cynologique Internationale (FCI) standard calls for dogs ideally between 1.5 and 3.0 kg (3.3 to 6.6 lbs.), although smaller ones are acceptable in the show ring. Pet-quality Chihuahuas (that is, those bred or purchased as companions rather than show dogs) often range above these weights, even above ten pounds if they have large bone structures or are allowed to become overweight. This does not mean that they are not purebred Chihuahuas; they do not meet the requirements to enter a conformation show. Oversized Chihuahuas are seen in some of the best, and worst, bloodlines. Typically the breed standard for both the long and short coat chihuahua will be identical except for the description of the coat.
Chihuahua breeders often use terms like miniature, teacup, tiny toy, apple headed, or deer headed to describe puppies. These terms are not recognized by the breed standards and are misleading.
Coat
The Kennel Club in the United Kingdom and the American Kennel Club in the United States only recognize two varieties of Chihuahua: the long-coat, and the smooth-coat, also referred to as short-haired. They are genetically the same breed. 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, the long-haired breed also typically sheds less than their short-haired counterparts. It may take up to two or more years before a full long-haired coat develops.
Colors
The American Kennel Club Chihuahua standard lists under color: "Any color-Solid, marked or splashed". This allows for all colors from solid blacks to solid whites, spotted, sabled, or a variety of other colors and patterns. A few examples are Fawn, Red, Cream, Chocolate, Blue, and Black. Merle coloring is a spotted coat. Patterns, all with or without white markings, include:
• Sable
• Irish spotting
• Dalmatian spotting
• Piebald spotting
• Extreme black spotting
• Brindle
• Masks
• Tan points
• Red
• White
• Black
• Merle
• Orange
• Fawn
• Tricolor
• Dark brown
• Blue
• extremely rare blue brindle
The merle coat pattern is not traditionally considered part of the breed standard. The United Kingdom Kennel Club decided in May 2007 not to register puppies with "Merle coat color in dogs" coloration due to the health risks associated with the gene responsible, and in December of that year formally amended the Breed Standard to say "Any color or mixture of colors but never merle (dapple)." The Fédération Cynologique Internationale, which represents the major kennel club of 84 countries also disqualified merle. Other countries' Kennel Clubs; including Canada, Australia, New Zealand, and Germany have also disqualified merle. However, in May 2008 the Chihuahua Club of America voted that merles will not be disqualified in the United States and they are fully registrable and able to compete in all American Kennel Club (AKC) events. Opponents of recognizing merle dogs in the breed standards suspect the coloration came about by modern genetic cross-breeding with other dogs, and not via natural genetic drift.
Classifying Chihuahua colors can be complicated due to the large number of possibilities. Examples would be a blue brindle or a chocolate and tan. Colors and patterns can combine and affect each other, resulting in a very high degree of variation. The classic Chihuahua color remains fawn. No color or pattern is considered more valuable than the others, although blue is considered rare.
Temperament
More than most other breeds, how a Chihuahua turns out depends mightily on the genetic temperament of his parents and grandparents (entire lines are social or antisocial) and how it is raised (socialization and training) when brought home. A Chihuahua must be chosen with care, as the temperament of its owner(s) can make a difference in the temperament of the pup. Ill tempered Chihuahuas can be easily provoked to attack, and are therefore generally unsuitable for homes with small children. The AKC describes the breed as, "A graceful, alert, swift-moving little dog with saucy expression, compact, and with terrier-like qualities of temperament." The breed tends to be fiercely loyal to one particular owner and in some cases may become over protective of the person, especially around other people or animals, but may be attached to more. They do not always get along with other breeds, and tend to have a "clannish" nature, often preferring the companionship of other Chihuahuas over other dogs. These traits generally make them unsuitable for households with children that are not patient and calm.
Chihuahuas crave attention, affection, exercise and being petted. They can be hyper and eager to please.They have a reputation as a "yappy" dog, which can be resolved with proper training. Chihuahuas with proper breeding are not "yappy"; the AKC standard calls for "a terrier-like attitude."
Health Disorders
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 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 plates 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 have moleras, or a soft spot in their skulls, and they are the only breed of dog to be born with an incomplete skull. The molera fills in with age, but great care needs to be taken during the first six months until the skull is fully formed. Some moleras do not close completely and will require extra care to prevent injury. 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. This is especially dangerous for puppies. Left unattended, hypoglycemia can lead to coma and death. This can be combated with frequent feedings (every three hours for very small or young puppies). Chihuahua owners should have a simple sugar supplement on hand to use in emergencies, such as, Nutri-Cal, Karo syrup or honey. These supplements can be rubbed on the gums and roof of the mouth to rapidly raise the blood sugar level. Signs of hypoglycemia include lethargy, sleepiness, low energy, uncoordinated walking, unfocused eyes and spasms of the neck muscles (or head pulling back or to the side). Chihuahuas are prone to eye infections or eye injury due to their large, round, protruding eyes and their relatively low ground clearance. Care should be taken to prevent visitors or children from poking the eyes. The eyes also water to remove dust or allergens that may get into the eye. Daily wiping will keep the eyes clean and prevent tear staining. Chihuahuas have a tendency to tremble but this is not a health issue, rather it takes place when the dog is stressed, excited or cold. One reason for this may be because small dogs have a higher metabolism than larger dogs and therefore dissipate heat faster. Due to this Chihuahuas often wear coats or sweaters when outside in the cold or in overly air-conditioned places. Chihuahuas often like to dig and snuggle down in blankets for sleeping.
Although figures often vary, as with any breed, the average lifespan range for a healthy Chihuahua is approximately 10 to 17 years.
Chihuahuas are sometimes picky eaters, and care must be taken to provide them with adequate nutrition. Chihuahuas could earn this reputation because they seem to find small unnoticed bits of food all day. Sometimes wet or fresh food can have the most appealing smell to these constant eaters. "They will eat when they are hungry" does not apply as Chihuahuas are prone to hypoglycemia and could be at a critical state if allowed to go too long without a meal. At the same time, care must be exercised not to overfeed them. Human food should be avoided. Due to their small size even tiny high fat or sugary treats can result in an overweight Chihuahua. Overweight Chihuahuas are susceptible to having an increased rate of joint injuries, tracheal collapse, chronic bronchitis, and shortened life span.
Chihuahuas are also known for a genetic condition called 'luxating Patella'. It's a genetic condition that can occur in all dogs, old or young, slim or overweight, particularly small dogs. In some dogs, the ridges forming the patellar groove are not shaped correctly, and a shallow groove is created. In a dog with shallow grooves, the patella will luxate (Slip out of place) sideways, especially toward the inside. This causes the leg to 'lock up' and will cause the chihuahua to hold its foot off the ground. When the patella luxates from the groove of the femur, it usually cannot return to its normal position until the quadriceps muscle relaxes and increases in length. This explains why the affected dog may be forced to hold his leg up for a few minutes or so after the initial displacement. While the muscles are contracted and the patella is luxated from its correct position, the joint is held in the flexed or bent position. The knee cap sliding across the femur can cause some pain, due to the bony ridges of the femur. Once out of position, the animal feels no discomfort and continues his activity.
Chihuahuas are also prone to some heart related disorders such as heart murmurs, i.e., extra heart sound produced due to turbulent blood flow and Pulmonic Stenosis in which the blood outflow from the heart's right ventricle is obstructed at the pulmonic valve.