Maybe diabetes. I have heard of this as a symptom of it.
You might see an endocrinologist if you have additional symptoms that may point to Cushing's syndrome or hypothyroidism (both can have the symptom of skin that bruises easily). You might also see your primary care physician to check your prothrombin (clotting) time.
Are you taking any anticoagulant (commonly known as blood thinners) medication or over the counter supplements, such as aspirin, Plavix, Warfarin, Coumadin, high doses of fish oil or flaxseed oil (fish and flax oil have mild anticoagulant effect)?
Sometimes I get bruises and I have no idea where they come from. If this is a constant issue, I would definitely seek a professional/doctor. This could be a sign of blood clots/disorders or things that are extremely dangerous if untreated/undiagnosed!