Painful red rash on sun exposed areas

Photodermatitis is an abnormal skin reaction to sunlight, or more specifically to ultraviolet (UV) rays. It can be acute (sudden) or chronic (ongoing). Photo dermatitis occurs when your immune system reacts to UV rays. You may develop a rash, blisters, or scaly patches. Exposure levels and reactions differ for every person. Several factors can make your skin sensitive to light UV rays, including having an inherited tendency to photosensitivity, taking certain medications, or being exposed to plants in the Apiaceal or Umbelliferae family, including weeds and edible plants, such as hogweed, cowbane, carrot, parsnip, dill, fennel, celery, and anise.