• Itching (pruritus) of the skin in exposed areas
• Skin redness or inflammation in the exposed area
• Tenderness of the skin in the exposed area
• Localized swelling of the skin
• Warmth of the exposed area (may occur)
• Skin lesion or rash at the site of exposure
  • Lesions of any type: redness, rash, papules (pimple-like), vesicles, and bullae (blisters)
  • May involve oozing, draining, or crusting
  • May become scaly, raw, or thickened

The diagnosis is primarily based on the skin appearance and a history of exposure to an irritant or an allergen.

According to the American Academy of Allergy, Asthma, and Immunology, "Patch testing is the gold standard for contact allergen identification." Allergy testing with skin patches may isolate the suspected allergen that is causing the reaction.

Patch testing is used for patients who have chronic, recurring contact dermatitis. It requires three office visits and must be done by a clinician with detailed experience in the procedures and interpretation of results. Patients should bring suspected materials with them, especially if they have already tested those materials on a small area of their skin and noticed a reaction.

Other tests may be used to rule out other possible causes, including skin lesion biopsy or culture of the skin lesion (see skin or mucosal biopsy culture).