Causes of itchy scalp include infections, allergies, dandruff, head lice and medical conditions, such as hypothyroidism, according to Healthgrades. Dandruff is the most common cause of itchy scalp.
Dandruff, referred to medically as seborrheic dermatitis, is a skin condition that causes flaky scales to form on the scalp, as noted by MedlinePlus. In addition to uncomfortable itching, patients with dandruff may experience skin lesions, hair loss and skin redness.
Head lice are small insects that live on the scalp, eyebrows and eyelashes, explains MedlinePlus. Spread through close contact with an infested person, lice appear similar to dandruff, but instead of flaking off the hair, they stay in place. Symptoms of head lice include small, red bumps in affected areas, extreme itching of the scalp, and tiny white specks on the bottom of each hair strand. Head lice do not carry or spread disease.
Hypothyroidism occurs when there is a deficiency of thyroid hormone in the body, as reported by Healthline. Low levels of thyroid hormone affect the body's normal metabolic functions, such as the maintenance of healthy muscles and cells. Along with itchy skin, patients with hypothyroidism may also experience symptoms such as weakness, depression, fatigue, constipation and brittle hair.