Diseases of the scalp include alopecia areata and lichen planus, according to Healthline. Alopecia areata is an autoimmune disorder where the body's immune system mistakenly attacks hair follicles, and lichen planus is a skin disease that causes hair loss and discoloration of the scalp.
Trichorrhexis nodosa is another type of scalp disease, usually caused by a person's genetics, states Healthline. This disease causes a person's hair to be weak and break easily. Seborrheic eczema is an inflammatory skin disease that can affect the scalp. This skin disease causes scaly and flaky patches on a person's scalp. Finally, psoriasis is another type of inflammatory skin condition that can affect the scalp. This disease results in red, scaly patches of skin.