How does scalp always itch?

Scalp itching is a physiological phenomenon of some people, for example, it is easy to be nervous, the scalp is tight or sometimes itchy when the weather is hot, so try to combine work and rest and relax. There is also because the scalp is sebaceous glands, sebum overflow parts, sebaceous glands secrete too much oil, hair will love oil, and sometimes it will stimulate the scalp and itch. There is also a secondary fungal infection because the oil secretion is strong, and the scalp is in a warm and humid environment, which is often said that there will be this malassezia infection on the skin surface, which will multiply in this greasy environment and stimulate the scalp to produce dandruff and scalp itching. There is also seborrheic dermatitis, which is prone to greasy scalp, dandruff, and even rash with hair loss. This condition is seborrheic dermatitis, accompanied by scalp itching. In another case, everything that comes into contact with the scalp is related. For example, if you change the shampoo, there may be an inappropriate shampoo. For example, some chemicals, such as baking hair, dyeing hair and perming hair, will also be accompanied by this itching feeling.