Infrared rays are the same as the rays from the sun that make your body feel very very warm. Infrared saunas are like going out in very very hot sun without getting any visible spectrum or damaging UV rays (though we do need UV rays to make vitamin D).

Also, I don't think many of use would have thought our fillings were safe if we knew that they contained 50% mercury. There is a reason why dentists call them silver fillings and not mercury amalgams.