 Patients who have experienced solar urticarial symptoms from a young age could mistakenly be thought to have erythropoietic protoporphyria.However, the main symptom for this disease is pain and patients with have been found to have abnormal levels of protoporphyrin in their blood while these levels are normal in SU patients.Finally, cholinergic urticaria, or urticaria induced by heat, can occasionally appear to be solar urticaria because the heat from the sun will cause a person with the disease to have a reaction.