The skin is the largest organ
in the body, and it is very sensitive.
Stress is known to alter our internal chemistry, and can cause a hormonal imbalance. This hormonal imbalance can significantly impact your overall health, and can affect the skin. So the answer to the question, can stress cause hives, is yes.
It would be good for you to deal with any underlying cause that might be triggering this off.
http://www.healthy-skin-guide.com/can-stress-cause-hives.