Scalp rashes are caused by seborrheic dermatitis, scalp psoriasis, eczema, Parkinson's disease, HIV and ringworm, according to WebMD. Less common causes are cradle cap, scleroderma, Ito syndrome and graft-versus-host disease, adds Healthline.
Seborrheic dermatitis on the scalp is called dandruff, states WebMD. Psoriasis occurs when the immune system triggers too many skin cells to grow on the scalp, and the cause of eczema is unknown. All three conditions present as redness, itching and flaking.
A fungus that lives and spreads on the top layer of the skin and on the hair causes ringworm infections, states WebMD. Ringworm is contagious and often looks like round, bald patches. The infection usually spreads outward while the inside of the circle clears up, making the infection look like a ring. Sometimes ringworm looks like dandruff, and some people with ringworm show no symptoms.
Scleroderma of the scalp is experienced as a hardening and tightening of patches of skin, explains Mayo Clinic. These patches might be shaped like ovals or straight lines and the skin feels tight with restricted movement. Ito syndrome is a rare birth defect that causes light patches of skin to develop on the body, states Healthline. Graft-versus-host disease is a skin rash that occurs after a bone marrow or stem cell transplant if the host rejects the transplanted tissue.