Wait: Do Japan actually forbid allergic people to donate blood?
Becouse Solar allergy (too broad term, the actual allergic related condition is called Solar Urticaria, while other sun related disturbs/illnesses are more akin to intollerances) isn't actually different then other allergies.
The medical part of the manga were a bit funky, but this is flat out wrong, unless there is a specific context.
Seems like the author wanted to make "solar allergy" some strange not understood condition, that despite the name is different then actual allergies, or they simply didn't research it except for it's existence.