Which of the following areas is most commonly affected by psoriasis?

Explanation: Psoriasis can develop at any age, but the most common age of onset is during adolescence and young adulthood. However, it can also appear for the first time later in life.

Incorrect choices: a. Infancy and early childhood - Psoriasis can occur in children, but it is less common in infancy and early childhood.

c. Middle age and older adulthood - While psoriasis can develop at any age, it is less common to have an onset in middle age and older adulthood.

d. Any age, as it is random - Although psoriasis can appear at any age, there is a higher prevalence of onset during adolescence and young adulthood.

Explanation: The presence of at least 3 typical psoriasis plaques on the body is one of the essential diagnostic criteria for confirming psoriasis. These plaques are characterized by well-defined, erythematous (red), raised lesions with silvery-white scales.

Incorrect choices: a. Positive skin biopsy showing eosinophils infiltration: While a skin biopsy may be performed to support the diagnosis of psoriasis, the presence of eosinophils is not specific to psoriasis and can be found in various skin conditions.

b. Family history of autoimmune diseases: A family history of autoimmune diseases may increase the risk of developing psoriasis, but it is not a definitive diagnostic criterion for the condition.

d. Elevated erythrocyte sedimentation rate (ESR) on blood test: An elevated ESR can indicate inflammation in the body, but it is not specific to psoriasis and may be present in other inflammatory conditions as well.