Leg infection usually referred as cellulitis can be a usual cause of swelling and it has distinct characteristics.
Cellulitis is a bacterial infection of the skin and the tissues beneath. It usually appears in areas where the skin has broken open, such as the skin near ulcers or surgical wounds.
In other circumstances, cellulitis occurs where there has been no skin break at all, such as with chronic leg swelling (edema)
The signs of cellulitis include redness, warmth, swelling, tenderness, and pain in the involved area.