Erythema Multiforme

Erythema multiforme is a reaction pattern in the skin that arises when the immune system responds unusually to a trigger — often an infection, a medication, or sometimes something that remains unidentified. The hallmark is the appearance of distinctive skin lesions, typically circular or target-shaped, that can appear suddenly and may affect the mouth, paws, or other areas where skin meets mucous membranes. Owners often notice red patches, blisters, or crusting that seem to have appeared over the course of hours to days, sometimes accompanied by a reluctance to eat if the mouth is involved. The pattern can range from mild skin changes to more widespread involvement, and understanding what might have preceded the onset can be an important part of making sense of what is happening. This page explores the signals that may suggest erythema multiforme, the underlying immune mechanisms that produce these skin changes, the investigations used to confirm the pattern and search for triggers, and the range of approaches available to manage the condition and support recovery.