Many 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. This is not a defect, it is a normal adaptation facilitating the passage through the birth canal and growth and development of the domed-type of forehead. The molera is predominant in the rounder heads often and is present in nearly all Chihuahua puppies. 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 if particularly large will require extra care to prevent injury. Many veterinarians are not familiar with Chihuahuas as a breed and mistakenly confuse a molera with hydrocephalus.
Some Chihuahuas can also be at risk for hypoglycemia, or low blood sugar, which is especially dangerous for puppies. Left unattended, hypoglycemia can lead to coma and death but can be avoided with frequent feedings, especially for chihuahuas who are younger, smaller or leaner. Chihuahua owners should have a simple sugar supplement on hand to use in emergencies. The one I like best is White Karo Syrup. The Karo Syrup can be mixed with warm water and syringed into the side of the mouth. Follow up with some type of protein. I like Gerber Toddler Chicken Sticks the best as they are easily eaten and digested by a young dog. Honey Nut Cheerios are also a good snack for puppies especially after playing hard. 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, fainting and seizures.
Although figures often vary, as with any breed, the average lifespan range for a healthy Chihuahua is between 10 and 18 years.