What your boyfriend seems to be having is called dermatographism. Dermatographism can be caused by stress
, tight or abrasive clothing, watches, glasses, energetic kissing, heat, cold, or anything that causes stress to the skin.
It can be treated by antihistamines or cromoglicate and sometimes steroids, as they prevent the histamine from causing the reaction. As the underlying cause of dermographism is not known, it can last for many years without relief.
I hope it helps.