as much as i would like to help you it would not be possible for me (or any medical professional) to diagnose your boyfriend's skin eruption based on your vague description.
my boyfriend has a rash on his arm that is spreading that is itchy and burning? what could it be? . he did inform that he had someone who has the same or looks like the same kind of rash wash his clothes. and when he got them back was when the flare up occurred. he has been putting calamine lotion and hydrocortisone cream on the area but it doesn't seem to be helping. he is also in an environment where there is no air and he is constantly hot and sweaty.