SAN FRANCISCO (CBS SF) — Those beautiful eyelash extensions that lengthen your lashes may actually harm your eyes.

There are new warnings that the glue used to attach them to the natural lashes poses a serious health risk. Some adhesives contain formaldehyde which can cause allergic reactions. In extreme cases, the glue can get onto the cornea and cause scarring, irritation and long-lasting damage.

Doctors also warn bacteria can grow on the fake lashes, leading to infections, and in some cases, cause real lashes to fall out.