Final answer:
Skin testing is used by allergists to investigate allergic contact dermatitis by injecting allergen extracts into the skin and measuring the wheal and flare response.
Step-by-step explanation:
Allergists use skin testing to investigate allergic contact dermatitis. In skin testing, allergen extracts are injected into the epidermis, and a positive result of a soft, pale swelling at the site surrounded by a red zone (called the wheal and flare response) usually occurs within 30 minutes. This response is caused by the release of histamine and granule mediators. The wheal and flare response is measured to identify the allergens that are causing the dermatitis.