Your mom may need a biopsy and some blood tests to make an accurate diagnosis. Discuss this option with your dermatologist or take a second opinion from another one near you. External factors like sunlight and heat can aggreveate some allergies. A biopsy will indicate the kind of reaction occuring in the skin and sometimes can diagnose the condition. A blood check up for blood cell counts, hemoglobin, thyroid disease, liver disease and kidney disease will rule out internal problems. Some diseases will respond well if diagnosed early and treated. Also ask your doctor to give some medicines for symptomatic relief for the itching. Warm regards. Dr. Rajdeep Mysore. Chirag Hospital Bangalore