Adhesives used to apply flash eyelashes may do more than help lengthen lashes. Those that are formaldehyde-based may also cause allergies and infections, the American Academy of Ophthalmology (AAO) warns in a news release.

Such risks may include infection of the cornea, infection of the eyelid, swelling of the eyelid, and permanent or temporary loss of eyelashes. A 2013 article published in Consumer Reports detailed several such cases of formaldehyde-based adhesives used with eyelash extensions.

As a result, the AAO urges caution in the use of these adhesives, and suggests that consumers make sure that the aesthetician is certified, works at a reputable establishment, and practices adequate hand washing and proper hygiene. In addition, the group suggests checking the ingredients of the adhesive before application.