Allergies are not the only reason that dogs itch. In fact, to properly diagnose hypersensitivity, one of the first things a veterinarian needs to do is to rule out other potential causes of itching. “Allergies are a diagnosis of exclusion,” says Donna Spector, DVM, DACVIM, an internal medicine specialist with a consulting practice in Deerfield, Illinois. A dog’s medical history can sometimes help his vet identify the reason for the dog’s itching, but in other cases, the history may be lacking (such as with a shelter dog).
In other cases, a good history may exist, but the picture it presents is muddled. Complicating the diagnostic task is the fact that some causes of itching may actually be a secondary effect of the dog’s allergy. For example, a dog may be itchy because he has a yeast infection (an overgrowth of an organism commonly found on even healthy dogs) – or he may have developed a yeast infection as a result of licking and chewing (due to an allergy), which created the conditions in which the yeast organism thrives. It may take some time and tests for your vet to sort it all out. Here are some of the other conditions that can cause dogs to itch.
– Bacterial infection (pyoderma)
– Contact dermatitis from exposure to a caustic agent
– Drug reaction
– Fungal infection (including yeast)
– Hyperadrenocorticism (Cushing’s disease – causes a secondary infection)
– Hypothyroidism (causes a secondary infection)
– Immune-mediated disorders – Includes conditions such as systemic lupus erythematosus (SLE)
– Liver, pancreatic, or renal disease
– Parasitic infection – Includes internal parasites, as well as external parasites such as fleas, ticks, and mites. Three main types of mites are most problematic: Cheyletiella (“walking dandruff”); Demodex canis (which causes demodicosis, also known as red mange or demodectic mange); and Sarcoptes scabiei canis (which causes scabies, also known as sarcoptic mange)
