Final answer:
Cellulitis most commonly affects the legs, where bacteria can enter through breaks in the skin and cause a painful, red rash along with symptoms such as fever and swelling.
Step-by-step explanation:
Cellulitis most commonly occurs on the legs. It is a bacterial infection of the skin and tissues beneath the skin. The bacteria can enter through a break in the skin, such as a scrape or cut. Once the bacteria have breached the skin barrier, as in the case of a scrape on the arm or when Mark scraped his lower leg, the infection can develop into cellulitis, presenting as a painful, red rash that is warm to the touch and may accompany a fever and swelling. The condition can affect different parts of the body but is often seen in the lower extremities due to factors like fluid retention and wounds on the legs that may not heal as quickly, particularly in individuals with compromised circulation or diabetes. Early treatment is crucial to prevent further spread of the infection.