Answer:
Food, insect bites, medications
Step-by-step explanation:
Foods you're allergic to (e.g. eggs), insects you're allergic to (e.g. bees), and medications you're allergic to (depends on the ingredients in the medicine). It can cause from sunlight as welll, but this is extremely rare considering being allergic to sunlight is also extremely rare, but the question asks for the "most common" causes.