Question: How do people get allergic to the Sun?

Leigh Kesler answered on 5 Mar 2019:

Sun allergies are the result of the immune system attacking the skin cells that have reacted to the sun. The reasons why people get allergies in general aren’t really known to us yet. An allergy is when the immune system thinks that an otherwise harmless thing in the body is harmful, and attacks it. This can result in a mild response (like hay fever) or a very serious response (like those with peanut allergies that go into anaphylactic shock). Some scientists think that allergies are related to how our bodies fight off other infections like stomach parasites, and hopefully someday soon we’ll have a better understanding of why this happens (and how to stop it!).