The most common causes of nighttime scalp itch include dandruff, seborrheic dermatitis, psoriasis, tinea capitis, head lice and allergic reactions, according to Cleveland Clinic. A more serious condition, such as a bacterial infection, can also cause an itchy scalp.
Dandruff and seborrheic dermatitis involve an overgrowth of yeast that causes the scalp to become inflamed, states Cleveland Clinic. This results in the itching and flaking of skin that are associated with dandruff. The treatment for mild cases is over-the-counter shampoos containing selenium or zinc pyrithione, such as Selsun Blue. Psoriasis is an autoimmune condition. It can be treated with special over-the-counter shampoos, but prescription-strength shampoos and topical steroids may be necessary. Over-the-counter medicated shampoo can also treat head lice, but ringworm of the scalp requires prescription-strength antifungal pills.