Although bruising is usually caused by bumping into something or by a fall, if you have several unexplained bruises anywhere on your body, please see your GP. My grand-daughter suddenly became bruised in several places and it seemed as if just looking at her would cause another one to appear, but after several tests she was diagnosed with Leukaemia. Unexplained bruising and really severe nosebleeds are just two of the signs to watch out for, plus extreme paleness and tiredness. Thankfully my grand-daughter responded to treatment and is now in remission. She was just 7 when she was diagnosed and she will be 14 before she can be given the 'all clear', but she is 12 soon and apart from an occasional glitch, she is recovering very well. To look at her you would never know she had this problem at all, and she continues to do really well at school despite missing almost 2 years on and off because of treatment.