Contact urticaria is a transient skin reaction that develops immediately after direct contact with a specific substance. This condition manifests as localized red, raised welts or hives on the skin. It is characterized by its rapid onset and quick resolution.
Understanding Contact Urticaria
Contact urticaria is an immediate hypersensitivity reaction, occurring when the skin encounters an offending agent. This reaction leads to the appearance of wheals—swollen, red areas with a pale center. These skin changes develop within minutes to an hour after exposure and resolve completely within 24 hours. Unlike allergic contact dermatitis, which presents hours to days later and persists longer, contact urticaria is distinguished by its immediate and temporary nature.
Common Causes and Triggers
Substances that trigger contact urticaria are categorized into immunologic and non-immunologic agents. Immunologic contact urticaria (ICU) involves a type I hypersensitivity reaction, meaning the immune system has been previously sensitized to the substance. Common immunologic triggers include natural rubber latex, animal dander, various food proteins such as those in nuts, eggs, and shellfish, and some medications.
Non-immunologic contact urticaria (NICU) is generally more common and does not require prior sensitization. These reactions occur directly from the irritating properties of the substance on the skin. Examples of non-immunologic triggers include stinging nettles, certain chemicals, preservatives, fragrances, flavorings, cosmetic ingredients, and medicaments.
Recognizing the Symptoms
Symptoms of contact urticaria appear following skin exposure to the trigger. These include itchy, red welts or hives directly at the site of contact. Burning, stinging, or tingling sensations may also occur.
While localized to the area of skin that touched the substance, the reaction can sometimes spread beyond the initial contact site. The hives are transient, fading within 24 hours. In cases of immunologic contact urticaria, widespread or systemic symptoms can occur, including wheezing, runny nose, watery eyes, swelling of the lips, hoarse throat, difficulty swallowing, or gastrointestinal disturbances. Severe reactions may progress to anaphylactic shock, necessitating immediate medical attention.
Diagnosis and Management
Diagnosing contact urticaria begins with a thorough medical history, focusing on potential exposures and the timing of symptom onset. To identify specific immunologic triggers, healthcare professionals may utilize skin prick tests. For non-standard or non-immunologic agents, scratch tests or open tests might be performed.
The most effective management involves avoiding the identified trigger. For symptomatic relief, oral antihistamines are often recommended, with second-generation options generally preferred. Applying cool compresses to the affected area can help alleviate itching and discomfort. In more severe reactions, topical corticosteroids might be prescribed. Seek immediate medical attention for widespread hives or signs of a severe systemic reaction, such as breathing difficulties, swelling of the lips, tongue, or throat, or any indications of anaphylaxis, which may require epinephrine.