Sudden itching all over the body may be caused by allergic diseases, adverse drug reactions, and dry skin. 1. Allergic diseases: Mistake to eat or touch some allergens appear allergic reaction, resulting in sudden itching all over the body, such as hives, eczema, atopic dermatitis and other skin diseases. 2. Adverse drug reactions: some drugs have the side effect of causing itchy skin, such as oral solution of metronidazole may lead to generalized itching adverse reactions. 3. Dry skin: affected by weather changes or environmental changes, such as wind blowing after exposure to the sun after the skin is dry and dehydrated, there will be itchy phenomenon. Suddenly itchy all over the body, there may be other factors, it is recommended to go to the regular hospital dermatology, clear cause, under the guidance of the doctor symptomatic treatment.