My mom has unknown skin allergy. heat, dry skin condition tend to trigger it. it only happens to upper body and especially around the waist. the symptom starts as a tiny dot and expands as a round pad in inches. it itches very much and lasts for week?

Possible urticaria: It's possible the itchy raised areas of skin around the waist are a form of urticaria, or hives. If there is an allergic reaction, then areas of irritation/rubbing of the skin, such as at the beltline, are common. Antihistamines such as Benadryl (diphenhydramine) will control itching from hives but may cause drowsiness. More important is to discuss with your doctor what may be causing this.