Most people can eat onion in food without any difficulties. Higher intakes of onion may worsen existing heartburn, though it does not seem to cause heartburn in people who do not already have it.⁴³ There are also isolated reports of allergy to onion, including among people with asthma,⁴⁴manifesting as skin rash and red, itchy eyes.

Onion is safe for use in children and, in small amounts in food, during pregnancy (though some pregnant women may have heartburn that onions could exacerbate) and nursing. It is unknown whether larger amounts of onion are safe during pregnancy and nursing. One study did find that baby rats nursing from mothers that were fed onion developed a taste for onion and suffered no ill effects.⁴⁵