What Causes A Raised Red Welt Whenever There Is Pressure On Skin?

My husband gets a raise, hot, red welt whenever there is pressure to any area of his skin that is very itchy and usually disappears by the next day or the day after. Example, he is an electrician and sometimes carries pipe on his shoulder and by the evening there will be a welt on his should where he carried the pipe. Likewise, if he leans on something putting pressure on a certain area, he will get the same thing. It happens anywhere on his body where there is a pressure point. He has no know allergies and this just started occuring within about the last year or so.