Which skin condition is potentially caused by a type III hypersensitivity reaction?

The condition that is potentially caused by a type III hypersensitivity reaction is the Arthus reaction. This type of hypersensitivity is characterized by immune complex formation, where antibodies bind to soluble antigens, leading to the precipitation of these complexes in various tissues and triggering an inflammatory response.

The Arthus reaction specifically manifests as localized inflammation and edema following repeated exposure to an antigen, such as after a vaccine. The localized skin reaction is typically seen as a result of these immune complexes depositing in the skin, which activates complement and attracts inflammatory cells, leading to tissue damage and the characteristic symptoms.

Chronic eczema, contact dermatitis, and psoriasis do not primarily involve type III hypersensitivity mechanisms. Chronic eczema is often associated with type I hypersensitivity reactions, particularly involving IgE-mediated responses. Contact dermatitis is a type IV hypersensitivity, which is a delayed hypersensitivity reaction mediated by T cells rather than immune complexes. Psoriasis has an autoimmune component but is primarily driven by T cell activation and involves a chronic inflammatory process rather than a type III hypersensitivity reaction.

Therefore, the Arthus reaction is the classic example of a condition resulting from a type III hypersensitivity reaction, making it the correct answer.