Of course, bruising can be caused by common trauma (injury). However, if the person did not hurt arm or leg, and the skin had a bruise, you should consult a doctor to be examined and, if necessary, to start to heal.

What caused the bruises on her arms

Bruising on hands evidence of subcutaneous hemorrhage due to violation of the integrity of the walls of the blood vessel. If we are talking about capillaries, bruises will be very minor (in most cases, almost invisible). That burst capillary, may testify only mild pain at the injury site of the vessel. If violated the integrity of the venous wall, blood flows a lot more.
It is easy to understand that the thicker was the bursting of Vienna, the more it will bruise.

Subcutaneous hemorrhage may be caused by various reasons. For example, this may happen due to the lack of elasticity, fragility of blood vessels. Also, the cause may be a bleeding disorder, the initial stage of varicose vein disease, hormonal changes in the body. Often bruises appear due to a lack of certain vitamins and minerals.
There are other causes of bruising on the hands, usually associated with various blood disorders.

Women due to physiological characteristics of the organism are often sharp fluctuations in hormonal levels. That is why they have bruises during menstruation, pregnancy, or breast-feeding.

Why do I get bruises on my legs

All of the above the causes of bruising can be fully applied also to the legs. However, feet have a constant load because of the need to withstand the weight of the body. Therefore, there are additional reasons for the lower limb, may appear bruiseI. Is, above all, large load, especially due to excess body weight or professional activities, for example, in athletes, porters, etc.; the need to stand for long periods, especially in uncomfortable shoes (the work of teachers, the seller).

In any case, it is advisable to consult a doctor. If possible, it is better to consult a qualified phlebologist (specialist in vein disease treatment). And, of course, necessary to reasonably measure the load on feet, and also to abandon the cramped, uncomfortable shoes (even at the expense of fashion).