Hi, it could be due to underlying disease.
Many skin conditions itch, including eczema (dermatitis), psoriasis, scabies, lice, chickenpox and hives. The itching usually affects specific areas and is accompanied by other signs, such as red, irritated skin or bumps and blisters.
Internal diseases. These include liver disease, malabsorption of wheat (celiac disease), kidney failure, iron deficiency anemia, thyroid problems and cancers, including leukemia and lymphoma. The itching usually affects the whole body. The skin may look otherwise normal except for the repeatedly scratched areas.
Consult Dermatologist for further evaluation....