She tried Caladryl lotion, and it didn't do much to relieve the itchiness, and the Benadryl pills (25 mg) didn't do much either. She usually gets it on her arms (biceps), and legs (thighs). She thought it might have been similar to a diaper rash due to perspiration.
One dermatologist took a plug of skin (she still has the scar from 8 years ago) thinking it would reveal what the cause was, but nothing was found.
She was the Doctor that recommended "Total Block" sunscreen, at $40.00 a bottle. She still got the rash after a week.
She just puts up with it now, enjoying her time on the Beach and suffering when she gets home.