The common causes of constant itching at the chin and neck are eczema and polymorphic solar lentigines. 1. Eczema: related to infection, endocrine, contact with allergic foods, inhalants, environmental changes and other internal and external factors, is a chronic inflammatory disease, can lead to local erythema, papules, mossy changes and other polymorphic skin lesions, accompanied by significant itching. 2. Polymorphic sun rash: it is a delayed hypersensitivity reaction induced by sunlight, the onset of which is related to the seasons, generally aggravated in spring and summer, and alleviated in fall and winter. It occurs in exposed areas such as the face, the front of the neck and other parts of the skin, can appear papules, pimples and other lesions, with significant itching. If the chin and neck are always itchy, you should go to the regular hospital in time to find out the cause of the disease, and choose the appropriate method of treatment under the guidance of a professional doctor.