The Chihuahua suffers from several skin conditions at higher rates than many other breeds. Among these are demodicosis, pattern baldness, and color dilution alopecia.
Demodicosis results in nasty, crusty infected lesions over the Chihuahua's head, legs, and body. The culprit is a mite that is usually present on the skin surface of all dogs; however, in some dogs, the population of this mite virtually explodes and wreaks havoc with a Chi's health. This condition is treatable, and even the most severe cases can generally be managed with medications.
Pattern baldness usually begins with a thinning of hair underneath the dog's neck, in her temple area, and on the chest, stomach, and back of the thighs. The thinning continues until these areas are completely void of all hair. Over time, the skin in these areas may darken and become scaly. The good news is that the condition doesn't seem to bother the dog in any way; the bad news is that there's really nothing that can be done to prevent or regrow the dog's hair.
Color Dilution Alopecia
Color dilution alopecia is an inherited loss of coat that tends to affect Chihuahuas with fawn or blue (light to dark gray) coloring the most. A Chi with this disease usually has small outbreaks of infected hair follicles (which appear as little bumps) on her back. As the disease progresses, the Chi's coat continues to thin until the age of two to three years, at which time the Chi's coat is bald on all the light-colored areas of her body. The exposed skin is susceptible to sunburn (use sunscreen!) and can be scaly in appearance. There is no way to regrow the lost hair; however, as with pattern baldness, the condition does not seem to cause the Chi any discomfort.