A dog's hair turns white when his body stops forming melanin. Melanin is the pigment that colors hair, and without it, hair is white. Just as it is with humans, aging is the most common cause of white hair in dogs. It is a normal and natural process and is not a cause for concern. There are, however, other potential causes involving medical conditions and more. Always check with your veterinarian if you have any concerns about your dog's health.
As a dog ages, formation of melanin gradually decreases causing his hair to turn gray, and eventually white. Larger dog breeds tend to age faster than smaller breeds, but on average, dogs enter their senior years between 7 and 10 years of age. You probably will notice graying and whitening on your dog's face first. Other signs of aging in dogs include thinning hair, tiring out more easily, sleeping more and a decrease in hearing.
According to Dr. Patrick Mahaney, a house call veterinarian in Los Angeles, California, premature graying on the face of a dog also could be caused by Cushing's disease, hypothyroidism and liver or kidney function problems. He recommends having your dog examined by your veterinarian and having her perform any blood work and testing she thinks is necessary. Some additional signs of both Cushing's disease and hypothyroidism include thinning hair, hair loss and skin problems. Kidney and liver function problems also may cause loss of appetite, weight loss and bloody urine, among other signs.
Genetics also play a role in a dog's coat color because a dog's genes determine his coat color and the pigmentary changes he may go through in life. There is a yet to be identified gene, called the progressive graying gene, that is known to cause premature graying of hair in dogs says Dr. Sheila M. Schmutz of the University of Saskatchewan in Saskatoon, Canada. Additionally, Dr. Mahaney states that pretty much anything has the potential to cause pigmentary changes to a dog's coat, including environmental exposure to sun, heat and cold.