There was a time when the word “highlighter” referred to a yellow marker that glided over important passages of Madame Bovary.

Let’s make that time the early 90s. Nirvana’s “Smells Like Teen Spirit” was inching its way up the charts, Clarence Thomas managed to make it onto the Supreme Court, and Marc Jacobs ignited the grunge trend on the Perry Ellis runway.

At that moment, I was a 30-year-old beauty editor at Mademoiselle magazine, a member of the “Do as I write, not as I do” school of makeup. Left to my own devices, I’d spackle on gobs of cream concealer, fooling nobody. Having virtually any beauty product at my disposal, I did my best to suppress the oil on my face with Erno Laszlo’s Sea Mud Deep Cleansing Bar and Shake-It foundation, and booklets of Papier Poudré. The bullies at Georgette Klinger’s facial salon would turn their magnifying lights on me, shifting my face roughly from side to side and sighing at the magnitude of work cut out for them.

Terry de Gunzburg had another solution to brighter-looking skin. A makeup artist in Paris and the creative and marketing director for Yves Saint Laurent Beauté, she visited my office in 1992. As she sat at our conference table, she pulled out a small gold pen with a clicker on one end and a white brush on the other. Flashing a mischievous smile that said, “Check this out,” she click-click-clicked until an almost rose-gold liquid oozed onto the brush. She gestured toward my boss, Felicia Milewicz, who jutted out her chin as if to say, “Do me first.”

With a few deft strokes, de Gunzburg’s pen and its sheer formula endowed Felicia’s face with the makeup equivalent of 12 hours’ sleep. That substance contained an unusual light-reflecting shimmer—and the term “highlighter” acquired a new meaning.

De Gunzburg had perfected the formula during her downtime at photo shoots. She began by combining a drop of Clinique foundation with toner and moisturizer in various proportions, testing each one on the back of her hand. “I’d add it in the curves around the mouth,” she tells me. “It was my recipe for revamping makeup on shoots. All the girls loved it.”

As she tried to commercialize her idea, a happy accident occurred. Instead of sending the usual concealer in a tube with a sponge tip, “one of the suppliers sent the brush-tipped one to me by mistake,” says de Gunzburg. “I asked our lab if they could put my mixture into this pen.”

Easier asked for than delivered.

Terry de Gunzburg, seen here with Carla Bruni-Sarkozy, was determined to make everyone look brighter than they had ever thought possible.

“We had to make the click of the pen compatible with just the right amount of formula, and the formula couldn’t be too thick or too fluid,” she says. “We kept having to change it up because [the supplier] did not get that I did not want coverage. We were using these super-expensive optical pigments that were among the first stages of soft focus with no color, and they didn’t understand that I didn’t want it opaque.” The goal: a product that melted into existing makeup instead of adding more layers. The word she used over and over was “enhancer.”

De Gunzburg estimates that it took at least 2,000 tries to get it right, but in the end, Touche Éclat—“a touch of glow”—was born. “I said, ‘It’s not a concealer; it’s a highlighter,’ but they”—meaning the suits at YSL Beauté—“didn’t know what ‘highlighter’ meant.”

It took me a minute to understand Touche Éclat, too. I brought that gold pen home from work in 1992 and practiced what we now know as highlighting. As someone who’d spent a good half-hour each morning covering up my red blotches and acne, this was upside-down-land. It took practice, requiring a change in attitude as well as technique. I left my shortcomings alone and dabbed a few strokes on my brow bone, cheekbones, and beneath my lower lip. It was as if someone had turned the lights on inside my face with a warm bulb.

Touche Éclat launched with one shade, which sounds preposterous if not culturally deaf and insulting. In the 90s, the beauty industry, with few exceptions, had not expanded its shades or its images beyond white women, despite the fact that Yves Saint Laurent himself had included women of color in his shows for 30 years. De Gunzburg remains adamant about the original product’s universal fit and appeal. “Because it was so sheer, it worked on everyone,” says de Gunzburg.

De Gunzburg followed up Touche Éclat with a series of innovations, including Effet Faux Cils, which she claims was the first mascara designed to imitate false eyelashes. (Trust me: this was at least a decade before the popularity of lash extensions.) She also developed one of the first makeup primers, Premier Teint, and the first color-saturated, liquid, matte lip color. She left YSL Beauté in 2000 to start her own makeup line, By Terry.

Touche Éclat now comes in 12 shades and, more than 30 years later, is the brand’s best-selling face product. One source claims that at its peak, a tube of Touche Éclat sold every six seconds; another puts it at every 10 seconds. I wasn’t there with a stopwatch, so I can’t confirm. It was one of a handful of beauty items to be included in the Museum of Modern Art’s 2017–18 exhibition “Items: Is Fashion Modern?”(The others were Bain de Soleil, Chanel No. 5, and Revlon’s Fire & Ice lipstick.)

Touche Éclat changed makeup and perhaps even minds. When its devotees sat in front of a mirror, examining their skin, they looked at themselves in a new way, accentuating the positive if not entirely eliminating the negative. Thanks to de Gunzburg and her gold pen, my skin came out of hiding. Sometimes, it even glowed.

Jane Larkworthy, the longtime beauty director at W magazine, is a Massachusetts-based writer