Well, generally speaking, tear gas is very harmful to your health, especially the eyes. First, you should know that tear gas is a blanket term that can be used for any of several chemical compounds that cause excessive tearing and irritation. As you know that it gets its name from its most obvious and characteristic effect. So tear gas can cause eye irritation and extreme tearing. And in some degree, it can just make your eyes become red and bloodshot. Also, the tearing and irritation are often so severe that people who have been exposed to tear gas cannot see properly and might not be able to keep their eyes open at all. By the way, your eyes and eyelids will swell noticeably.