Why do my blood vessels in my hand keep breaking?

Usually trauma. There are many veins on the top of the hand which are relatively close to the surface of the skin and are prone to be injured.Trauma to the area (this could be a simple banging of your hand without you even being aware) could result in beaking of the vein leading to a black and blue area. Also medications such as aspirin, blood thinners and even vitamin e. Flaxseed and and nsaids can cause this.