Eyelash extensions, an increasingly popular beauty trend, can cause serious and long-lasting health problems, according to a new investigation.

Salons enhance eyelashes through extensions by gluing single synthetic fibers, one-by-one, on to natural eyelashes.

A Consumer Reports investigation found many salons use formaldehyde-based glues to attach the synthetic lashes. Formaldehyde is a chemical that can cause allergic reactions and has been classified as a cancer-causing substance by the U.S. Environmental Protection Agency.

Consumer Reports also discovered eyelash extensions can cause a woman's real eyelashes to fall out. Doctors at the College of Optometrists in England warn extensions cause "excessive tension on the hair shaft," leading to hair falling out or even causing hair production to stop.

Other health dangers associated with eyelash extensions include:

  • Conjunctivitis
  • Keratitis/Cornea irritation
  • Allergic reactions
  • Infection

Consumer Reports recommends using mascara instead. However, researchers say women should replace mascara every three months and never share it with someone else.