Have you heard of rosacea, look it up and let us know if this sounds possible. And yes, multivitamins do have niacin in them. Usually the dose isn't too high to cause this but you may be sensitive to it. I had this problem when I was taking niacin supplements (straight one's, not multivitamin) but it occurred allover and I would get this rush of heat throughout my body, pulsating heat waves with sweating! My palms and other parts of my body would get BRIGHT red! Good luck, this must be difficult for you. Go to your PCP and/or a dermatologist.