Thanks for posting your query.
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
This can happen for a variety of reasons, from vitamin deficiency
in your diet to leukemia
, which is a type of cancer. Bruising of this type is also sometimes normal for a person, you should have it checked out so you can rule out bigger, more serious problems.
I advice 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.
Wishing you good health
Dr saurabh gupta