What Causes Rashes Breaking Into Bumps After Laser Treatments?

Hi iv had four laser treatments on my face - sides and chin area. I break out in a rash after each treatment which calms down but then i get lots of red bumps under the skin that look like welts and are mildly itchy. These persist for weeks after treatment and seem to flareup of their own accord. They are not only on treaed arwas they also seem to spead to neighbouring areas too. Please help.