“Some lash glues contain formaldehyde, which can irritate the eyes,” says Taylor. “If applied poorly, extensions can cause lashes to become brittle and break off.” That being said, getting lash extensions can be perfectly safe as long as you take the right precautions. Taylor recommends not overusing extensions, which can lead to hair loss, researching where you schedule your appointment to ensure you’re going somewhere safe, and doing a patch test to determine if you’re allergic to any extension glue.