Any wound may be classified according to the number of skin layers affected. Damage limited to the epidermis is regarded as a superficial wound which will heal rapidly by regeneration of epithelial cells. A partial thickness wound involves the deeper dermal layer and includes vessel damage. Its repair is more complex. A full thickness wound affects the subcutaneous fat layer and beyond. Its healing will require the synthesis of new connective tissue and it takes longer to heal because it contracts, whereas partial thickness wounds do not.