Muscle strain occurs when muscles are stressed, overworked, or injured due to physical activity or labor.
A hematoma is a collection of blood in the tissue outside of a damaged blood vessel, usually after an injury.
Cellulitis, a bacterial infection of the skin, causes red, tender skin that is usually swollen and warm.
A skin abscess, or boil, is a swollen, painful, red and warm lump of skin that may rupture and drain pus.
Bruises, or contusions, cause skin discoloration, swelling and tenderness.
Epidermal (sebaceous) cysts are painless, moveable lumps that form beneath the skin's surface.