Boyfriend and siblings have scabies. I don't have the rash but I'm itching a lot, will permethrin cream work even if I haven't developed a rash yet?

Treat immediately. The "rash" with scabies is due to violent scratching. EVERYBODY with contact MUST be correctly treated.This includes all girlfriends and everybody in his home. YOU ALSO HAVE SCABIES. Permethrin must be applied to every inch of skin from ears to toes. The itch is due to allergic reaction against the mites. Usually it is 2 or 3 months from initial infestation to onset of itch, and a few weeks to end.