“Something bad has happened. I’ve got eyelash extensions,” singer and actress Kristin Chenoweth confessed on the “Late Show with David Letterman” last year while wearing large dark sunglasses, and visibly drowsy on Benadryl. “Here’s the problem: The glue has formaldehyde in it, and I’m allergic,” Chenoweth said. “I swelled up and I’m sneezing. . . . It looks like I have lips on my eyelids.”

The Broadway star is far from alone in her quest for longer, thicker eyelashes. Women have been enhancing their lashes since before the days of Cleopatra. Mascara, marketed since 1917, is a multibillion-dollar industry. False eyelashes went mainstream in the 1960s (thanks in part to Twiggy). The market has benefited from promotion by celebrity trendsetters including Nicki Minaj and Rihanna. The Kardashian sisters recently announced their line of false eyelashes and tweeted, “Faking fuller lashes are a thing of the past. For 2013 faux lashes are being worn BIG and without apology.”

But the quest for beauty can come at a price. Eyelash extensions—single synthetic fibers glued one by one to natural eyelashes—are usually fixed in place by formaldehyde-based adhesives or other biologic glues. The adhesives can cause allergic reactions, as can the solvents used to remove them. In addition, cosmetic eyelash enhancers carry a risk of bacterial and fungal infection.

Eyelash extensions have also been reported to cause irritation to the conjunctiva (conjunctivitis) or cornea (keratitis). The irritation can be caused by direct contact from the lashes themselves or hypersensitivity to the substances used to attach them. Among beauty treatments, eyelash extensions account for the greatest number of eye-clinic consultations in Japan, where they have been very widely used.

Women are also learning that eyelash extensions can cause hair loss resulting in eyelashes so thin that women feel they have no choice but to continue the cycle. Indeed, the College of Optometrists in England has warned that “repeated use of eyelash extensions can cause traction alopecia, a condition where the hair falls out due to excessive tension placed on the hair shaft. As a result, this can damage the hair follicle, which can slow down and even cease production of hair.”

Even temporary false eyelashes can cause trouble. Pulling false eyelashes off can also remove natural lashes if those hairs get in the way, the traction alopecia similar to that caused by extensions. False lashes can also trap dirt and bacteria, creating irritation and infection, and a reaction to the glue can cause allergic swelling of the eyelids much like the reaction Chenoweth reported. There was no puzzle to solve when mystery writer Janet Evanovich experienced problems after attending the premier of “One for the Money” last January. “They put false eyelashes on me,” Evanovich blogged, “and I had an allergic reaction to the glue. On the plus side, my eyes didn’t swell up and break out until after I saw the movie.”

Some ophthalmologists report seeing patients with allergic reactions and infections as a result of eyelash enhancements. “Sometimes just the irritation from the glue used can lead women to rub or tug on their lashes,” says Philip R. Rizzuto, M.D., secretary for communications for the American Academy of Ophthalmology. The condition is called madarosis.

Eyelash vanity is reaching even more perilous heights. On the Internet, advertisements for eyelash-transplant cosmetic surgery promise to “thicken and enhance the appearance of eyelashes.” The operation, touted as a “minor outpatient procedure” by some, involves removing hair follicles from the back of the scalp and replacing the grafts on eyelids.

Beware, too, of the latest eyelash-bling trends. One involves threading tiny glass beads onto ultrathin copper or silver wire that is bent to conform to the shape of your eye and applied with an adhesive directly above the eyelashes. Another involves glueing crystals onto eyelash extensions. It doesn’t take an expert to see trouble coming when sharp objects are near the eye.

Our advice? Stick to mascara, and use it safely:

• Wash your hands before you apply mascara.
• Replace your mascara tube every three months.
• Don’t borrow, lend, or share it.
• Never add water to the tube; if your mascara dries out, throw it away.
• Avoid makeup-counter application, even with a fresh wand.
• If you see any sign of infection or irritation, stop using mascara until it clears.

Orly Avitzur is medical adviser, Consumer Reports and blogs at the Consumer Reports Health Blog.