Lots of things we put in the eye can cause allergies. The most common are eye drops. For example, someone has Viral Conjunctivitis. Their provider prescribes antibiotic drops. For one, antibiotics don’t kill viruses (effectiveness is pure “zero”). Next, lot of those drops cause allergic reactions. So you a) pay money, for b) useless medicine, that c) makes you worse.
Other substances that cause contact allergies include make-up and hair sprays. We make the diagnosis by detective work. Sometimes we see signs of allergies on the eyelids, which is a wonderful clue but not always present.
Symptoms are itching and tearing, not pain (which would suggest more serious eye disease). Treatment is to stop using the offending substance.