Sudden itching can have many causes, including dry skin, insect bites, allergic reactions, skin conditions (such as eczema or hives), heat rash, scabies, psoriasis, or exposure to irritants like certain plants or chemicals. It can also be triggered by environmental factors, nerve-related issues, internal diseases (like liver or kidney problems), or psychological factors such as stress or anxiety. Sometimes, medications or new skincare products can also cause itching. If the itching is widespread, intense, or accompanied by other symptoms like a rash, swelling, or pain, it may be important to seek medical advice to identify the exact cause and receive appropriate treatment.