Hair loss in dogs can be due to a variety of factors. Certain breeds are predisposed to alopecia or hair loss. Some of the more common reasons for alopecia include fungal infection, parasite infestation, endocrine disease such as hypothyroidism and hyperadrenocorticism, and bacterial or yeast infection of the skin associated with underlying skin hypersensitivity due to flea allergies, food allergies or atopic dermatitis.
Younger dogs with hair loss can suffer from a parasite infestation such as demodectic mange. Correctly diagnosing the most common underlying cause for pruritic hair loss takes a lot of time and very strict effort. A flea/tick hypersensitivity trial will require use of a flea and tick preventative every 2 weeks for at least 4 treatments before determining its effectiveness. A food trial will require a completely new food with a novel protein and carbohydrate source. Many over the counter limited ingredient foods are not really limited ingredient and the labels must be read with extreme caution. Prescription hypoallergenic foods although costly are a much more reliable source of limited ingredients. Your dog will need to be placed strictly on this new diet with no other food of any kind for a minimum of 2 months before assessing if there has been at least 50% improvement. If there is 50% improvement, then the trial should be continued. If there is less than 50% improvement the trial can be discontinued. All food sources need to be reviewed carefully as people often forget about things such as pill pockets and treats that can completely disrupt the food trial. Environmental allergy testing can consist of a blood test or intradermal testing. Pending the results of these tests cats can be started on customized allergen immunotherapy vaccines. These vaccines require consistent use and results may not be seen for up to one year. Failure of these vaccines can only be determined after a year. Some owners who do not see results from any of the above mentioned will go for immunosuppressive medications such as Atopica. Immunosuppressive medications also have their side effects so careful consideration should be given before starting any of these medications.
Dogs are also much more prone to secondary bacterial infections and may need concurrent antibiotics while starting any of the above mentioned treatments.