Differential Diagnosis for Rash/Hives from Sun Exposure

• Single most likely diagnosis
  • Polymorphic Light Eruption (PMLE): This is the most common condition causing a rash or hives due to sun exposure. It occurs in response to ultraviolet (UV) radiation and can appear as an itchy, bumpy, or blistering rash.
• Other Likely diagnoses
  • Solar Urticaria: A rare condition characterized by hives or itchy wheals that appear after exposure to sunlight. It's an immune system reaction to sunlight.
  • Phototoxicity: This occurs when certain medications or substances react with UV radiation, leading to a rash or blistering of the skin.
  • Photoallergic Contact Dermatitis: An allergic reaction to certain substances (like sunscreen or fragrances) that occurs when they are exposed to sunlight.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Porphyria Cutanea Tarda: A genetic disorder that can cause blistering of the skin when exposed to sunlight, due to a deficiency in an enzyme involved in the production of heme.
  • Erythropoietic Protoporphyria (EPP): Another genetic disorder that leads to severe burning pain and blistering after sun exposure, due to an accumulation of protoporphyrin in the skin.
• Rare diagnoses
  • Chronic Actinic Dermatitis: A rare condition characterized by a persistent, itchy rash in sun-exposed areas, often seen in individuals with a history of prolonged sun exposure.
  • Actinic Prurigo: A rare skin condition that causes an itchy, bumpy rash in sun-exposed areas, more commonly seen in individuals with a family history of the condition.
  • Hydroa Vacciniforme: A rare condition that causes blistering and scarring of the skin after sun exposure, often seen in children and young adults.