Dog Skin Rash Diagnosis

A dog skin rash is extremely irritating and can lead to excessive scratching, biting and hair loss. There are many causes for dog skin rash, some contagious and some resulting from immune system suppression or deficiencies. Many of these disorders have telltale signs for diagnosis, but others may require further testing to determine the cause of the skin rash, and any underlying conditions that may be leading to the problem.


One of the common causes of dog skin rash is allergies. This includes allergic reactions to food products, medication, shampoos or flea powder. Generally, an allergic reaction of this nature will cause a rash to develop over all or most of the dog's body. When dealing with allergies, it may be best to think about any changes that may have recently affected your dog. If you have changed food, started a new medication or recently bathed the dog with flea or tick control products, one of these may be the culprit.

Exposure to Toxins

A reaction to toxic plants, chemicals or substances will usually cause a localized skin rash and appear very suddenly. This is sometimes referred to as contact dermatitis. The rash may be of varying degrees, but could be severe enough to cause hair loss or scabs. If one or more spots develop, you can attempt to discover any toxins the dog may have come into contact with, either in the house or outside. These could include oil or residue from certain plants, household cleaners, insects such as spiders or pesticides.

Flea Allergy Dermatitis

Fleas not only cause severe itching and irritation in dogs, but can lead to what's called flea allergy dermatitis. Hot spots can develop due to excessive biting, licking and scratching from the allergic reaction to flea saliva. Hot spots are specific areas where hair may fall out, and bumps and bleeding may occur. There are several other conditions which can cause similar symptoms in dogs. To determine if flea allergy dermatitis is the cause of your dog's skin rash, attempt to get rid of the fleas and see if the skin condition improves.

Bacterial Infection

Bacterial infections cause itchy, yellow pustules that may become ulcerated, and lead to odorous, crusty spots with hair loss. Signs of this disorder are usually found between the dog's toes, on the callouses of the elbows, on the chin or in skin folds of obese dogs, or on dogs that have wrinkles in the skin.


Ringworm is not caused by worms, but rather by a fungal infection. Ringworm can usually be fought by the immune system of a healthy dog, so signs of this infection have a tendency to show up in younger dogs or dogs with an underlying condition. Patches with hair loss, often circular in nature, may have a dry, crusty appearance and grow larger over time. Ringworm most often appears on the head and legs.


There are a few common types of mange in dogs. Mange is caused by mites and can lead to intense itching with scaly or crusty patches similar to ringworm. The front portion of the body is usually affected the most severely by this infection.