Psoriasis involves unusually active activity of which skin cells?

• A. Melanocytes are overactive
• B. Langerhans cells proliferate
• C. Fibroblasts produce excess collagen
• D. Basal cells are unusually active

Answer: (D)

In psoriasis, the epidermis shows rapid keratinocyte proliferation, and the cells in the deepest layer of the epidermis—the basal keratinocytes—are unusually active. This basal-layer hyperactivity drives the overall epidermal thickening (acanthosis) and the accelerated turnover that produces the characteristic plaques and silvery scales. Basal cells are the source of new keratinocytes, so their heightened activity directly leads to the abnormal skin growth seen in psoriasis. The other cell types listed aren’t the drivers here: melanocytes handle pigment but aren’t proliferating abnormally; Langerhans cells are immune sentinels in the epidermis, not the source of epidermal hyperplasia; fibroblasts in the dermis produce collagen and relate to connective tissue, not the epidermal cell turnover.