Explanation: The primary etiological factor in psoriasis is a genetic predisposition. Psoriasis has a strong hereditary component, and individuals with a family history of the condition are at a higher risk of developing it. While environmental triggers can exacerbate psoriasis symptoms, the condition itself is primarily influenced by genetic factors.

Incorrect choices: a. Bacterial infection: Psoriasis is not caused by a bacterial infection. It is an autoimmune condition characterized by an overactive immune response, leading to inflammation and skin cell overproduction.

b. Fungal overgrowth: Fungal overgrowth is not a cause of psoriasis. Psoriasis is not related to fungal infections and has a different underlying mechanism.

d. Allergic reaction: While certain allergens may exacerbate psoriasis symptoms in some individuals, an allergic reaction is not the primary cause of psoriasis. The condition's pathophysiology is rooted in immune system dysfunction rather than allergic responses.