 [ Symptoms ] is a long amount of time in the heat worse for you if you have high blood pressure  is extended amounts of time in the heat such as in a sauna where it is hot enough for a smart phone to over heat and power off with out being in use bad for you if you have high blood pressure can the long amount of time in the heat cause your blood pressure to go up even more [ Disease ] hives do not spread when you scratch them although there are types of hives that can be caused by skin pressure most of the time hives are caused by something you have eating breathed or touched i know hundreds of possibilities and will respond to oral antihistamines