What can lead to a sun allergy?

Meds and fruits. There are a number of medications (usually antibiotics) that if taken and then a person is exposed to sunshine (uva), they develop a photo-allergic or photo-toxic rash. This can also be seen after handling fresh limes in the sunshine. After applying topical nsaids or even some sunscreens, a photo allergic contact dermatitis can occur. A dermatologist can easily assess these.