What is the reason why the skin is always itchy

The skin is always itchy, this situation may be an allergic dermatitis, or chronic urticaria, may also be systemic factors caused by skin itching. Of course, most of the first two cases are caused by allergic factors, allergic factors are actually a lot, most of the general ingested factors, that is, after eating some allergic food, and caused by skin itching. In addition, exposure to some environmental factors, such as living or working environment, there are some allergens, can also cause systemic itching. In addition, breathing, if breathing some allergic particles, may cause systemic itching. Systemic factors may generally belong to the kidney or liver function abnormalities, or thyroid function abnormalities, will cause systemic itching.