What Is The Treatment For Hives In The Arm And Chest?

The last few years I have started to get hives usually into my second week of my holiday. They start on my arms then onto my chest. I have lived abroad before and have had the odd holiday and not got them at all. I do, however, have sensitive skin and I was wondering if it could be the sun lotion? I don't sun bath and don't feel sweaty or uncomfortable in the sun so I don't think it is a heat rash.