When bruising occurs, the skin often turns red immediately, but the injury doesn't turn black or purple for one to two days, according to KidsHealth. Most bruises take about two weeks to fade and go through several color changes, becoming less tender as they heal.
The initial red color is due to the blood that collects under the skin, but KidsHealth indicates the changes in hemoglobin cause the dark purple or black color often associated with a bruise. About a week later, it fades to green or yellow and then becomes brown or yellow-brown before fading completely.
Bruises form when the capillaries, the small blood vessels near the surface of the skin, break and allow blood to leak under the skin, according to Mayo Clinic. Unless the skin breaks, bruises rarely need a bandage. Self-care for bruises includes use of ice and elevation, resting the injury and using over-the-counter pain medication to reduce swelling. A lump forming over a bruise indicates a hematoma and a doctor should examine the injury.
Most bruises heal without requiring further treatment, according to WebMD. Severe bruising and swelling that occur within 30 minutes of the injury sometimes indicate a more serious injury. Potential causes of this type of bruising include sprains and fractures.