Eyeliner can make our eyes seem brighter. And it can also make our eyes look either bigger or smaller and emphasize the shape of our eyes. Many people use eyeliner for this make them for beautiful and energetic. But as to the side effect, maybe the eyeliner is not very easy to get rid of when we want to wipe out them.
Eyeliner is a part of the makeup. It will make our eyes more noticeable. Makeup will make us look more beautiful. So does the eyeliner. I haven't heard any side effect of the eyeliner if you are not allergic to makeup and choose a qualified product. But if you are a new starter, you should be careful not to get the eyeliner into your eyes.