Rashes are very common in dogs, and are almost never an emergency on their own. When a rash is accompanied by difficulty breathing, profuse vomiting, or collapse, this is an emergency and could be a sign of anaphylaxis.
Rash can be secondary to many conditions, such as hypothyroidism, Cushing’s disease, allergies, autoimmune disease, and cancer. If a rash gets worse or does not go away after one week, veterinary attention is warranted.
A rash is generally due to inflammation, irritation, or a defect in the skin.
Rash varies widely in severity and can range from slightly reddened skin to weeping sores. Some rashes can spread to encompass larger areas of skin, be itchy, purulent (pus-filled), and foul-smelling. Hair loss may be observed with hypothyroidism, welts with allergic reactions, and purulent exudate with hot spots.
Visual examination can help diagnose a rash, but testing is necessary to determine the underlying cause. Diagnostics include skin cytology to check for microorganisms, blood tests to check for underlying metabolic disease, biopsies to rule out cancer, and allergy testing.
Treatment varies widely depending on the underlying cause of the rash. Examples include oral antibiotics, anti-inflammatories, antiparasitic medications, topical ointments, antihistamines, antifungals, anti-itch medication, and surgical removal of lesions.
A swelling under the skin may be mistaken for a rash.