The No. 1 response to my informal survey of Frenchwomen about the years of magical aging is not gaining weight. Ever. If a Frenchwoman happens to see an additional kilogram or two on her bathroom scale, she will do whatever is necessary to force the needle back where it belongs. “I keep my weight steady, no ups and downs,” Ms. Caron said. “I avoid all excess.” She claims to eat all kinds of food in small  her friends say minuscule  portions, and she doesn’t drink alcohol. It’s not so much that “French Women Don’t Get Fat,” as the title of Mireille Guiliano’s best seller had it. Rather, Frenchwomen won’t get fat.

Not that they exercise. When my husband and I arrived in Paris and asked our personal banker  everyone has one  for a gym recommendation, her response was: “Why? Gyms are a form of torture.” It seems the only acceptable way to burn calories is to walk.

Image Ellen Barkin, 56, was smooth-cheeked at Cannes. Credit... Matt Sayles/Associated Press

If Frenchwomen don’t walk enough to stay en forme, there is always a pill, a lotion, a machine or a treatment to do the trick. Pharmacies have counters full of diet and figure-improving remedies. One cream promises “accelerated reduction in the areas resistant to diet” (hips, thighs and buttocks). Capsules assure a flatter stomach in four weeks. A poster recently plastered all over Paris Métro stations advertises a tiny Slendertone “Electronic Muscle Stimulation” belt that claims to provide, in a single session, the equivalent of 120 abdominal crunches. (It’s available in the United States, too.)

Frenchwomen also recommend facials, massages and spa “cures” in their campaign against wrinkles, cellulite and saggy bottoms, bellies and breasts. One spa favorite is thalassotherapy, the seawater-based treatment that originated in France. It involves water jets, seaweed wraps, mud baths and sea-fog inhalation, meant to improve circulation, promote sleep, tone muscles and reduce cellulite. Some women are resourceful enough  or have legitimate medical reasons, like arthritis  to get doctors’ prescriptions for weeks at their favorite spa. That means government health insurance covers much of the bill.

As for makeup, Frenchwomen of almost every age (except those teenagers) regard less as best. Heavy foundation has a tendency to emphasize wrinkles and pores, and most women avoid it in favor of a bit of blush. Those who do use foundation make sure that it blends with the skin, often by applying it just after moisturizing. The idea is to look as natural as possible: a little color on the eyelids, mascara, maybe a bit of eyeliner and lip gloss.