A rash develops in some people when they touch certain plants and then go into the sun. The sunlight converts a chemical in these plants to an allergen, causing an immune system reaction similar to a poison ivy, oak, or sumac rash (allergic contact dermatitis). The rash only develops in areas exposed to sunlight.

These plants include:

• Celery, parsley, parsnip, carrot, dill, and fennel.
• Citrus plants (bergamot, lemon, lime).
• Queen Anne's lace.
• Rue and angelica.
• Fig.