People with photosensitivity have an immunological response to light, usually sunlight. They typically
break out in a rash when exposed to sunlight; how much exposure it takes to cause a reaction varies from
person to person. Several conditions, such as erythropoietic protoporphyria and polymorphous light eruption,
share the common symptom of hypersensitivity to light—also typically sunlight.
People taking certain prescription drugs (sulfonamides, tetracycline, and thiazide
diuretics) or herbs (St. John’s wort, for example) and
those with systemic lupus erythematosus have increased susceptibility to
adverse effects from sun exposure.