Skin allergic reactions

Skin allergic reactions: Types and mechanisms

The skin is one of the main "target organs" for allergic reactions. It can respond to allergens that entered the body through food or medication, as well as to substances that come into direct contact with its surface. Most allergic rashes are accompanied by intense itching.

Main types of allergic skin lesions

• Urticaria (hives): This is a classic immediate-type allergic reaction (IgE-mediated). It is characterized by the sudden appearance of itchy wheals that disappear quickly. It can be triggered by food, medications, insect bites.
• Angioedema (Quincke's edema): Similar in mechanism to urticaria, but the swelling occurs in deeper layers of the skin and subcutaneous tissue. It most often affects the lips, eyelids, tongue. Swelling of the larynx is life‑threatening.
• Atopic dermatitis (eczema): This is a chronic allergic skin disease, based on a complex mechanism that includes both IgE-mediated and cellular reactions. It is characterized by dryness, redness, scaling, and severe itching.
• Allergic contact dermatitis: This is a delayed-type allergic reaction (T‑cell mediated). The rash appears 24–72 hours after skin contact with an allergen (e.g., nickel in jewelry, cosmetic ingredients, latex). It manifests as redness, swelling, and small vesicles at the contact site.

It is important to distinguish allergic contact dermatitis from simple irritant dermatitis, which is not an allergy but a direct skin injury caused by an aggressive substance. For general information about rashes, see the corresponding section.