Allergic skin hives or urticaria, are red, itchy bumps near the surface of the skin. Like many other allergies, they are the result of overproduction of histamine and any reaction can be caused by a wide variety of things.
During much of the year, plants produce pollen and mold knows no season and may occur anytime. Plants release pollen in order to fertilize other plants. Not all of those particles reach their intended targets and some enter the airways of people. The same goes for mold, which can find its way into the nose or mouth through many routes.