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Hypersensitivity (also called hypersensitivity reaction or intolerance) is an abnormal physiological condition in which there is an undesirable and adverse immune response to an antigen. [ 1 ] [ 2 ] It is an abnormality in the immune system that causes immune diseases including allergies and autoimmunity .
Type III hypersensitivity, in the Gell and Coombs classification of allergic reactions, occurs when there is accumulation of immune complexes (antigen-antibody complexes) that have not been adequately cleared by innate immune cells, giving rise to an inflammatory response and attraction of leukocytes.
If left untreated, the skin may darken and become leathery and cracked. [4] Pain can also be present. Dermatitis can occur anywhere on the skin, but is most common on the hands (22% of people), scattered across the body (18%), or on the face (17%). [5]
Skin allergies frequently cause rashes, or swelling and inflammation within the skin, in what is known as a "weal and flare" reaction characteristic of hives and angioedema. [ 29 ] With insect stings, a large local reaction may occur in the form of an area of skin redness greater than 10 cm in size that can last one to two days. [ 30 ]
Type IV hypersensitivity, in the Gell and Coombs classification of allergic reactions, often called delayed-type hypersensitivity, is a type of hypersensitivity reaction that can take a day or more to develop. [1] Unlike the other types, it is not humoral (not antibody-mediated) but rather is a type of cell-mediated response.
Contact dermatitis is a type of acute or chronic inflammation of the skin caused by exposure to chemical or physical agents. [1] Symptoms of contact dermatitis can include itchy or dry skin, a red rash, bumps, blisters, or swelling. These rashes are not contagious or life-threatening, but can be very uncomfortable.
According to the National Psoriasis Foundation, skin cells typically grow and fall off within a month, but in people with psoriasis, skin cells go through this process in just a few days. Instead ...
Cutaneous small-vessel vasculitis (CSVV) is inflammation of small blood vessels, usually accompanied by small lumps beneath the skin. [1]: 831 [2] The condition is also known as hypersensitivity vasculitis, cutaneous leukocytoclastic vasculitis, hypersensitivity angiitis, cutaneous leukocytoclastic angiitis, cutaneous necrotizing vasculitis and cutaneous necrotizing venulitis, [3]