This ingredient’s super power? It can hold 1,000 times its own weight in water. (That’s sort of like you holding up a whale. Crazy, right?). Hyaluronic acid is naturally present within your entire body and has the consistency of a viscous gel. It acts as a lubricant to help your joints, muscles, and nerves function smoothly. Think of it like the oil in a car engine.

Hyaluronic acid also serves another key function in optimal skin health. It strengthens your moisture barrier, which is the outermost layer of your skin and your first line of defense against environmental aggressors. Think of your moisture barrier as the roof of a house. When it’s intact, it protects everything inside, but when it’s leaky, damage occurs. When your moisture barrier is intact, your skin appears and feels smooth, soft, and plump. If your moisture barrier is damaged, your skin looks dry and rough. (Think of dry skin cells flaking off your skin as a tile slipping off the roof of the house.) The more damaged your moisture barrier, the harder it is to reverse issues like dehydration, wrinkles, hyperpigmentation, and breakouts. Hyaluronic acid fills in the spaces between your skin’s essential support structures, keeping your moisture barrier strong and cushioned.

"Hyaluronic acid is a must-have in your moisturier, regardless of your skin type, because it’s the ultimate hydrator,” say Dr. Henry. Every skin type would look its most youthful, plump, and radiant with an optimised moisture barrier. Your moisture barrier can be compromised daily by environmental factors like indoor heating, sun exposure, dehydration, pollution, and dirt. Additionally, your body naturally loses about one pint of water a day, which can affect your skin’s level of hydration. Also keep in mind that your ability to retain water and naturally produce hyaluronic acid declines as you age, which can exacerbate increased dryness, fine lines, wrinkles, and sagging. (Babies have such soft, plump skin because they have a ton of hyaluronic acid in their cute, pinchable bodies.)

Hyaluronic acid is a key ingredient in many moisturisers and serums and should be used day and night. But don’t be scared that this type of intense hydration has to come in a thick cream. Case in point: Moisture Surge™ 100H Auto-Replenishing Hydrator, which has a lightweight gel texture. This serum-in-a-jar actually has two types of hyaluronic acid—one that works immediately on the uppermost layers of your skin, and another variant that penetrates deeper. “The formula features different sizes of hyaluronic acid, so that some are able to penetrate and hydrate deeper into the skin while others plump the surface of the skin,” explains Dr. Henry. Use it daily for immediate and long-lasting hydration, or tap it over makeup for a midday shot of extra moisture. Another hyaluronic acid superstar: Smart Clinical Repair™Lifting Face + Neck Cream, which is not only loaded with it, but it also helps reduce the four major signs of ageing with its powerful blend of peptides and moisturising ingredients.