What causes bruises on the legs and arms with no apparent causes?

I would have that checked. It could be a symptom of a bigger problem -- everything from diabetes to leukemia.

See your doctor. Could be a problem with your blood having a hard time clotting. If you're a male, it could be hemophilia. Don't panic, just go in and be seen by your doctor.

The most basic cause of it is that your blood is not clotting properly, so it is spreading under the skin, and creating a bruise. The more important question is why your blood is not clotting properly. This can happen for a variety of reasons, from too many leafy greens in your diet (they have a blood thinning effect) to leukemia, which is a type of cancer. Bruising of this type is also sometimes normal for a person, but the main thing to know about it is that you should have it checked out so you can rule out bigger, more serious problems. I know it's easy to dismiss something like this, and figure it can wait, but I would really urge you to see a doctor about it quite soon. Easy bruising is indicative of so many disease processes that it needs to be investigated promptly.

i would like to know that to, every time i turn around, my son has bruises on his legs and i ask him what happened and he dont know. it has me worried.

You might want to have you hemoglobin level checked, you be anemic. Even small little bumps into soft furniture that you wouldn't ordinarily notice will cause bruises if you levels are low. They may prescribe iron supplements. Or it may be something as serious as luekemia, you would have bruises all though if that was the case. Anyway you should see a doctor because something is not right

Stop what you're doing right now and go see a doctor.

First of all are you on any medications especially aspirin or any other pain killers? Are the bruises on the sun exposed areas? Bruises in these areas are seen mainly in older people due to thinning of skin and then most minor of traumas can cause bruisies. Is your bleeding time and clotting time normal.... get it investigated. Meet your doctor to find the exact reason. If its a single lesions dont worry too much.... Sometimes we do forget about a injury and 2 - 3 days later we find a bruise there. If they are too many meet the doc.