Is pruritus (body) a common allergy symptom? are allergy induced pruritus alleviated with anti histamines? how different from miliara rubra?

Yes: Allergy is usually associated with itching at the affected organ but most itching are not caused by allergies. Dry skin is by far the most common cause for itching without a skin rash. If the itching is caused by allergies (but not contact allergy), antihistamine in sufficient doses would work. In contact allergy involving the skin, topical cortisone works far better.