What is a physical allergy?

Physical allergy or physical urticaria refers to a range of skin conditions in which hives develop in response to a physical stimulus without involvement of an allergen or antibody-mediated immune response. The exact mechanism, in some cases, is not well understood yet.

These conditions are classified based on the specific triggering factor, and common types of physical allergies include:

1. Cold urticaria: Hives develop upon exposure to cold temperatures, such as cold water, cold air, or even handling cold objects.

2. Heat urticaria: Hives form in response to heat, such as hot water, warm clothing, or high temperatures.

3. Solar urticaria: Also known as sun allergy, hives develop after exposure to sunlight or ultraviolet (UV) radiation.

4. Pressure urticaria: Hives arise at sites of sustained pressure or friction, like tight clothing, belts, or prolonged lying down.

5. Vibration urticaria: Hives occur due to vibrations, such as from using power tools or riding a bike.

6. Dermatographism: Hives develop when the skin is scratched or stroked firmly.

7. Water urticaria: Hives form upon contact with water, regardless of its temperature.

The mechanism behind physical allergies often involves the release of histamine and other inflammatory mediators directly from cells like mast cells, without the involvement of antibodies and allergens. In certain cases, UV radiation-triggered production of reactive oxygen species may also contribute to histamine release.

Management of physical allergies typically involves identifying and avoiding the specific triggers. In some cases, antihistamines or other medications may be necessary to control symptoms.