My son gets a red rash on his arms after being outside in the sun. What causes this and what can I do to prevent it?

Answers from Lawrence E. Gibson, M.D.

Sun rash and sun allergy are terms often used to describe a number of conditions in which an itchy red rash occurs on skin that's been exposed to sunlight. A common form of sun rash is polymorphic light eruption, also known as sun poisoning.

Some people have a hereditary type of sun rash, while others develop signs and symptoms only when triggered by another factor — such as certain types of medications or skin exposure to certain plants, such as limes or wild parsnip.

People who have severe sun sensitivity may need to take preventive measures, such as:

  • Limiting exposure. Avoid spending time in the sun, especially when the sun's rays are most intense — between 10 a.m. and 4 p.m. Some people may react to sunlight shining through glass, in which case it may help to use window films in your car and home.
  • Using sunscreen. Use a high-SPF sunscreen that specifically blocks both ultraviolet A and ultraviolet B rays. Apply sunscreen generously, and reapply every two hours — or more often if you're swimming or perspiring.
  • Covering up. Wear a broad-brimmed hat and cover your arms and legs with clothing that's tightly woven or specifically designed to protect from the sun.
  • Avoiding triggers. Avoid touching wild parsnip, lime juice and other triggers while in the sun.
Oct. 28, 2015 See more Expert Answers