What Could Cause Red Patches All Over The Body?

hi doctor..a friend of mine is suffering from red pathches all over the body..the doctor whom we consulted has suggested it was due to the throat infection and has prescribed dipsalic ointment..now the problem is the patches have spread all over the body..can u tl me what is the reason for this and what are the remedies for it how can it be cured and what are the diets to be followed?