Numbness can be caused by a variety of things. How would know which?

It depends. We diagnose numbness depending upon what part of the body is numb-may be due to a disorder of the brain, spinal cord, nerve root, or peripheral nerve. Each part of the nervous system may cause a characteristic pattern of numbness. For example, a stroke on the right side of the brain could cause the left side of the body to be numb. Carpal tunnel syndrome numbness of the thumb, index, middle finger.