Once a bruise has “come out” or it is fading it is usually too late to treat. However, initially you can significantly reduce bruising if you apply pressure to a bleed or to a sprain, an icebag and where it is on a limb, rest and elevate it. Most spontaneous bruising is due to medications (i.e. Aspirin, Clopidogrel or Warfarin) or unrecognised trauma, particularly in older peoples skin
External visible bruising rarely needs medical attention. However, seek medical attention fast where there is spontaneous purple skin discolouration (which has appeared in the last minutes or hours). This can be a sign of meningitis and may warrant a 999 call. Non urgent spontaneous bruising can be investigated by your GP (where it has gone on for days or weeks).