Cholinergic urticaria is a sub category of physical urticaria (aka hives).  Like many rashes, this can be brought on by a hypersensitive reaction with increased body heat.  Any condition that raises the body temperature can cause the onset of this rash. Sometimes, exercise induced sweating will be the reason for the outbreak. For some individuals, this will only occur in the winter months when  their body temperature rises if not acclimated to the sudden heat.  One way to reduce the outbreak is to consistently exercise to break a sweat before the onset of cold weather and to consistently maintain this regimen. There are other causes of urticaria or hives as well 

To obtain more information about this and many other conditions, visit the offices at Center for Dermatology, Laser and Cosmetic Surgery at  our two conveniently located offices in northeast Philadelphia and Narberth.