My Husband Had A Umbilical Hernia Repair On Oct 28th.

My husband had a umbilical hernia repair on Oct 28th. On nov 5 he started breaking out in hives. The incision looks good and there is no drainage and he is not running any fevers. He stopped taking his pain medication (Percocet) on nov 4th. Could the hives be caused by the mesh or could it be a delayed reaction to the pain medication? Thank you