A 59-year-old man presents to the nurse practitioner with a poorly demarcated, warm, erythematous area on his lower right leg. It is associated with edema and produces tenderness on palpation. What is the pathogenesis of cellulitis?

Choice A reason: Cellulitis is a bacterial infection of the dermis and subcutaneous tissues, most commonly caused by group A beta-hemolytic Streptococcus and Staphylococcus aureus. It presents with warmth, erythema, swelling, and tenderness, often with systemic symptoms. The infection typically enters through breaks in the skin. Choice B reason: This describes acne or folliculitis, which involves inflammation of pilosebaceous units. Cellulitis affects deeper layers of the skin and is not limited to hair follicles. Choice C reason: This describes the pathogenesis of psoriasis, a chronic inflammatory skin condition. Psoriasis involves keratinocyte hyperproliferation, not infection. Choice D reason: Psychological stress and environmental allergens may exacerbate certain dermatologic conditions like eczema or urticaria, but they are not causative factors in cellulitis, which is infectious in origin.