Generalised itching has many etiologies. Physiological itching can occur in pregnancy and the elderly, as can itching from allergens such as unsuitable temperature and humidity, mental stress and anxiety, and exposure to medication and food.
If there is only itching without lesions and other discomfort it may be pruritus, if lesions are present it may be a skin condition such as generalised eczema, atopic dermatitis, urticaria, itchy rash, insect bite dermatitis, scabies, etc. Severe and persistent itching can also be caused by systemic diseases such as primary biliary cirrhosis, chronic kidney disease, true erythrocytosis, diabetes, HIV infection, tumours, etc.