What skin condition is characterized by a wide, diffuse area of erythematous skin that is warm and tender, especially on the lower leg?

Cellulitis is a common skin condition that presents as a wide, diffuse area of erythematous skin, which is characteristically warm and tender to the touch. It commonly affects the lower leg and is caused by an infection of the skin and the underlying soft tissue, often from bacteria such as Streptococcus or Staphylococcus. The affected area is typically swollen and can be painful, with symptoms often including fever and chills due to the body's immune response to the infection.

In contrast, diabetic ulcers usually present as localized lesions on the feet or lower legs and are not characterized by widespread redness and warmth. Kaposi's sarcoma, while it may appear as lesions on the skin, is generally associated with vascular tumors and does not typically present with diffuse erythema. Necrotizing fasciitis, although it involves severe infections similar to cellulitis, does not usually begin with a diffuse erythematous pattern; instead, it often starts as localized pain and may evidence rapid progression, systemic toxicity, and severe pain out of proportion to the physical exam findings.