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To diagnose eczema, a physician will perform a complete physical examination and compile a thorough medical history. Other tests may also be performed. For example, a physician may conduct patch testing that exposes a patient’s skin to various substances to determine if any of the substances inflame the skin, which would be characteristic of contact dermatitis. Allergy testing may occasionally be necessary to identify allergens that may trigger atopic dermatitis.

A physician may also take a scraping of the rash and examine it under a microscope to make sure it is not caused by a fungus. Eczema is usually diagnosed if three conditions are present:

• Characteristic scaly rash
• Intense itching
• Personal or family history of asthma, hay fever or other allergies