Occasionally, following a transplant procedure, the donor’s immune cells recognize the recipient’s tissues as foreign and trigger a multisystem disorder called graft-versus-host disease (GVHD). Occurring commonly after bone marrow or stem cell transplants performed to treat some blood cancers, GVHD may even follow solid organ transplants and is, in essence, the reverse of transplant rejection. Now, researchers have clarified the pathogenesis of the characteristic skin changes in chronic GVHD.