The skin inflammation associated with itching is an important symptom and to correctly diagnose atopic dermatitis it is important to know in what context, at what times, and how much the dog or cat itches.

Skin inflammation can be aggravated by bacterial (Staphylococcus) or yeast (Malassezia) infections, which also need treatment. Recurrent ear infections are also often caused by allergy (in over 75% of cases).

Signs such as redness, superficial scratch wounds, discoloration of the fur (from excessive licking / grooming) and hair loss also reflect the severity of the allergy. Depending on the duration and severity of the disorder, lesions can vary between erythema (redness), hyperkeratosis (keratinisation) and lichenification (thickening) of the skin. Occasionally, atopic dogs and cats will have watery eyes, asthma or sneeze. Sometimes there may be digestive symptoms.

Symptoms can be present throughout the year or only during a particular season, depending on the allergens that trigger the allergic reaction. The first symptoms typically occur by 1–3 years of age (in around 75% of all cases). Occasionally, symptoms occur in animals under 6 months of age.