Chances are, you've encountered the ingredient called benzalkonium chloride, which can
irritate skin. It's often contained in hand sanitizers, so your efforts to fend off the flu may cause your hands to
break out in itchiness and redness. Another place you'll find it in: as a preservative in many eye drops, says Neeta Ogden, MD, spokesperson for the American College of Allergy, Asthma and Immunology (ACAAI). Using them could cause
similar symptoms in the eye. Ogden adds that because your eye doctor may not realize you're reacting to that specific ingredient, she may give you different eye drops in an effort clear things up. Catch is, they may contain the same preservative, which will only prolong symptoms. Work with your pharmacist to find BC-free drops, Ogden says. As for hand sanitizers, if you're allergic, scan the ingredient list to make sure yours doesn't contain it (some will advertise that they contain no "benzalkonium chloride").
