Hi, High histamine suggests an allergy. You should avoid sweating, use talcum powder, use cotton shirts, apply steroid skin ointment & take anti allergic medicine like Allegra. This would relieve allergic rash. If rash aggravates with this, other possible condition causing the symptoms can be- Itching on the back with red bumps while you mostly sleep on the back gives the possibility of sweating making a moist & warm condition of the skin that favours fungal infection. I would advise frequent cleaning of back to make it dry, sitting up to give some air to back, spindle candid talcum powder & use multifungin ointment when you sit or lie on side. If no result in a week you need oral medications after confirming the type of infection and visit a dermatologist. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Vasudha Jayant Athavale, General & Family Physician