ABC News' Abbie Boudreau and Bethany Owings report:

Eyelash extensions are among the hottest new trends out of Hollywood, but some experts warn that there are risks.

Actress Kristin Chenoweth had an allergic reaction, joking with David Letterman while wearing sunglasses during an interview shortly after the procedure, "It looks like I have lips on my eyelids."

Experts say eyelash extensions are typically made out of synthetic fibers that are glued to the natural eyelashes, many times with formaldehyde-based adhesives, which can cause allergic reactions for some.

And Consumer Reports is warning women this week that longer lashes might not be worth it.

"The hidden dangers with eyelash extensions include infection, allergic reaction, irritation and loss of your natural lashes," Dr. Orly Avitzur, a Tarrytown, N.Y., neurologist and medical adviser to Consumer Reports, told ABC News.

Tiffany Howard, a mother of two, got eyelash extensions to achieve superstar Adele's popular cat-eye look.

"I wanted to feel that if I walked out of the house with nothing else, my eyes looked good," Howard, 44, of Encino, Calif., said.

At first, she loved her new lashes, but then they started growing out.

"I needed to take them out and, when I did, unfortunately, out came my lashes with my extensions," Howard said.

Dr. Neda Shamie, an associate professor of ophthalmology at Doheny Eye Institute in Beverly Hills, Calif., said, "Any chemical exposure to the cornea being so fragile in some ways or susceptible to scarring and irritations and infection, it could be harmful."

But the Association for Damage-Free Eyelash Extensions defends the practice, saying, "Properly applied eyelash extensions are not dangerous," and that the "adhesive should not contain formaldehyde," and "hypoallergenic adhesives are available."

Howard's lashes eventually grew back, although she says the beauty treatment was "absolutely not" worth it.