Clotting is normal, but clots can be dangerous when they do not dissolve on their own. Once clots form, they can travel to other parts of your body, causing harm. Some risk factors put certain people at higher risk for developing a blood clot. Though sometimes, a blood clot in a vein can occur with no apparent underlying risk factor.
Stop the Clot, the health site, says there are several symptoms of a blood clot in the leg or arm.