Sudden itchy skin is mainly considered to be related to environmental changes, contact dermatitis, urticaria and other factors. 1. Environmental changes: Sudden and drastic changes in temperature can cause certain stimulation to the skin, resulting in itching and other uncomfortable symptoms. 2. Contact dermatitis: Sudden contact with allergens or irritants can trigger an allergic or irritant reaction, resulting in itchy skin. 3. Urticaria: When ingesting, inhaling, or contacting certain allergens, such as drugs, food, pollen, etc., can cause urticaria, which manifests itself as a sudden itchiness of the skin, accompanied by doughnut-like lesions. 4. Other factors: such as diabetes, can lead to elevated blood sugar, affecting the peripheral nerve endings, and then the symptoms of itchy skin. Itchy skin symptoms, there may be other reasons, it is recommended to consult a doctor to confirm the diagnosis, follow the doctor’s instructions for treatment.