Graft versus host disease is also called GVHD. It is a problem that may happen after a stem cell or bone marrow transplant. GVHD is when the transplant or graft cells think the normal or host cells are foreign and attack them. This happens more when the transplant comes from a donor who is not related. Graft versus host disease can happen right away or a long time after transplant. It can affect many body systems, like your skin, liver, eyes, lungs, or stomach and bowels.