There are many reasons for sudden itching on the body, such as urticaria, contact dermatitis, eczema, insect bite dermatitis, drug rashes, fungal infections, diabetes and so on. 1. Urticaria: the skin mucosa due to a temporary increase in vascular permeability, the occurrence of limited edema will cause skin tingling, itching and other symptoms, will lead to sudden itching. 2. Contact dermatitis: contact with sensitizing or irritating substances can cause contact dermatitis at the contact site, causing erythema, blisters, itching, papules, etc., which can also lead to sudden itching. 3. Eczema: Inflammatory skin reactions caused by internal and external stimuli can cause sudden itching. 4. Insect bite dermatitis: Inflammatory reaction of the skin caused by mosquito bites can also cause sudden itching. 5. Drug rashes: allergic reactions caused by systemic or localized medications can also lead to sudden itching. 6. Fungal infections: fungal infections caused by ringworm, jock itch, tinea capitis, tinea cruris and other diseases, can also lead to sudden itching. 7. diabetes: diabetes is a chronic endocrine disease, may also lead to diabetic neuropathy, can also lead to sudden itching. Suddenly itchy body, there may be other reasons, need to go to the hospital in time to check, clear cause.