An itchy scalp when you sweat may be caused by cholinergic urticaria, seborrheic dermatitis, or other diseases such as eczema. 1. Seborrheic dermatitis: the etiology of seborrheic dermatitis is not yet clear, and it is considered to be related to age, gender, hormone levels, diet, and late-night factors. The main symptoms of patients are yellow-red patches on the head and face, itchy, greasy scales, etc., which will lead to the phenomenon of itchy scalp as soon as the patient sweats. 2. Cholinergic urticaria: cholinergic urticaria is mainly due to the cholinergic nerve impulses, the patient will appear small air masses, self-conscious itching and other symptoms. It will cause the patient to appear as soon as the sweaty scalp itchy phenomenon, in addition, cholinergic urticaria patients will also appear headache, tearing, nausea and other symptoms. 3. Other: eczema, contact dermatitis and other diseases can also lead to patients with an itchy sweaty scalp phenomenon. Patients with symptoms of itchy sweaty scalp, should seek medical attention in a timely manner, in accordance with the doctor’s instructions for treatment.