Why Is My Dog Losing Hair?

by Silvia
(Colorado)

Reader Question: Reasons for Dog Hair Loss

My 13 year old Labrador has been losing extremely large patches of hair with a crust at the shaft of the hair. He was treated for allergies and gave him antibiotics for infection. Nothing happened. He was treated for mange and has not gotten better. He has been like this for almost two months now.

Vet Suggestion: How Dog Hair Loss is Diagnosed

Hi Silvia,

I am sorry to hear about your dog’s chronic skin condition. It is hard for me to comment on what might be going on because the list of potential causes is quite long, and I am unsure of what tests have already been run. I can tell you how I approach cases like this, however.

My first step is to run a few simple diagnostic tests, usually a skin scraping to look for mange mites, skin cytology to diagnose any skin infections and determine whether yeast or bacteria are to blame, and a fungal culture for ringworm. The ringworm test can take a few weeks to complete, so while we’re waiting for those results, I’ll treat for anything that I’ve found (e.g., a yeast infection) and often put the patient on a broad spectrum parasiticide like Revolution to kill some of the parasites that can be hard to find on diagnostic tests.

If these initial tests all come back negative and the dog isn’t doing significantly better on whatever treatment I’ve prescribed, the next typical step is to investigate the possibility of allergies. Dogs can be allergic to environmental triggers (pollen, mold, etc.) or to ingredients in their food. Diagnosing a food allergy requires a strict food trial lasting at least 6-8 weeks during which the dog eats nothing but a prescription diet that contains novel protein and carbohydrate sources or proteins that have been hydrolyzed. Determining what environmental triggers a dog might be responding to ideally is done through intradermal skin testing, although blood testing can be considered for some individuals.

If allergies seem unlikely or test results are all normal, I will then recommend skin biopsies.

As you can see, getting to the bottom of some types of skin problems in dogs is not a simple endeavor. Making an appointment with a veterinary dermatologist is a good option if you want answers as quickly as possible.

Best of luck,

Jennifer Coates, DVM