Hello, Thanks for your query. If you are pretty sure that you haven t injured your wrist I can think of Spontaneous bruising. A spontaneous bruise, also known as an easy bruise, is one that occurs on its own and the person has no recollection of what caused the bruise. This type of bruise can begin to form as you watch it. It usually begins with the area swelling up and within an hour the bruise begins to appear. Many times the area will be sensitive to the touch, or feel as if you had hit it against a hard surface. For other people, a spontaneous bruise may occur from lightly tapping the skin, a touch that normally doesn t cause a bruise to occur. There are many reasons why a spontaneous bruising can occur such as: -Medications, both over-the-counter and prescription can cause bruising to occur. Over-the-counter pain relievers such as ibuprofen, naproxen and aspirin interfere with blood clotting and cause bleeding into the skin tissues. Prescription drugs such as warfarin and clopidogrel also reduce the bloods ability to clot, causing easy bruising. Cortisone medications such as prednisone can cause capillaries to become fragile and break easily. If you are taking any of these medications it can be the cause. I do hope that you have found something helpful and I will be glad to answer any further query. Take care