Which sites are most commonly affected by psoriasis?

• A. Face and trunk
• B. Scalp, elbows, knees, and extensor surfaces
• C. Palms only
• D. Mucous membranes only

Answer: (B)

Psoriasis most often presents with plaques on the scalp and on extensor surfaces such as the elbows and knees. This pattern reflects the disease’s tendency to affect areas of friction and rapid skin turnover, making scalp and extensor sites the most frequently involved. While it can involve the trunk or face, those areas are less consistently affected than the scalp, elbows, and knees. Palms can be involved in palmoplantar psoriasis, but a presentation limited to the palms alone is not as typical, and mucous membranes are rarely involved in classic plaque psoriasis. Therefore, the combination of scalp, elbows, knees, and other extensor surfaces is the best description of the most commonly affected sites.