Allergies are a common cause of hives since an allergic reaction can trigger the immune system response that results in trapped fluid beneath the skin.An allergic reaction can occur due to something you ingested or were exposed to through the air.hoto Credit pollen image by asb from Fotolia.com. Allergies are a common cause of hives since an allergic reaction can trigger the immune system response that results in trapped fluid beneath the skin. An allergic reaction can occur due to something you ingested or were exposed to through the air.
The median nerve, which runs through the arm and hand, can cause swelling pain and numbness if injured. Ulnar nerve injury Damage to the ulnar nerve causes swelling, pain and numbness in the forearm, hand, and ring and little fingers.
8. A Brain Tumor Is a Rare Cause of a Numb Arm. Relax -- brain tumors are quite unusual. While it's important not to panic at the first sign of a numb arm, it could be caused, in some very rare cases, by a brain tumor. A brain tumor can cause loss of sensation and movement in an arm.