My grandmother is 85 years old. it's been 6 months that she has an itchy scalp.it gets better when she take allergy pills. what can she do to stop it?

Itchy skin is common: Itchy skin is common, especially in the elderly. Commonly dry skin or mild irritation is the reason, however a prolonged, persistent rash can be serious. Get her seen by a dermatologist and biopsied, particularly to rule out skin cancer (basal cell, squamous cell, etc.) and other proliferative diseases such as T cell lymphoma - which incidentally can take several biopsies before it is discovered.