What is the distinguishing characteristic of psoriasis?

Psoriasis is primarily characterized by silvery scaly lesions that are typically found on extensor surfaces of the body, such as elbows and knees. These plaques develop due to accelerated skin cell turnover, leading to the buildup of cells on the surface, which results in the distinct silvery color and scaling as the skin cells die and accumulate. The extensor surfaces are particularly affected, distinguishing psoriasis from other skin conditions that may present with different characteristics or distribution patterns.

In contrast, the other choices describe conditions or lesions that do not align with psoriasis. For instance, lesions on flexor surfaces are more commonly associated with eczema rather than psoriasis. Flat brown spots are characteristic of conditions such as lentigines or age spots, while red, itchy patches can indicate various dermatological conditions, including allergic reactions or infections, but lack the specific scaling and appearance associated with psoriasis. Understanding these nuances helps in the accurate identification and differentiation of skin disorders.