Short answer? Apply your vitamin C first, then pat on your HA. Vitamin C (especially L-ascorbic acid) is notoriously unstable—it loses potency when it’s exposed to air, light, and water—which is why you want to apply it on clean, dry skin right after washing. You’ll also want to let it dry completely, as piling on products right after could potentially deactivate the vitamin C. 

You don’t need to be as precious with hyaluronic acid. Yes, applying on damp skin will make it easier for the humectant to pull in water, but it can also draw in that moisture from the surrounding environment, too. Let’s not forget: Hyaluronic acid can hold up to 1,000 times its weight in water, and you don’t necessarily have to provide that water yourself. “That way, you don’t need to worry that HA needs to go directly onto damp skin,” says board-certified dermatologist Ife J. Rodney, M.D., FAAD, founding director of Eternal Dermatology + Aesthetics.  

So you can apply your vitamin C first, let it dry completely, then apply your hyaluronic acid. Just remember to top everything off with a moisturizer—you still want to seal in the HA to lock in the hydration. 

Or, if you do want to apply your HA on damp skin to maximize its benefits, board-certified dermatologist Ava Shamban, M.D., founder of SkinFive, still recommends applying your vitamin C serum and letting it dry completely. “The highly reactive nature and low pH of vitamin C in serum form will usually allow it to penetrate the cleansed, dry skin quickly,” she says. After it dries, apply a water-based hydrating toner or essence (here are our favorites), then pat your hyaluronic acid serum onto the freshly misted skin. Again, follow up with a moisturizer to lock in the hydration. 

Hyaluronic acid is a humectant, meaning it has the ability to attract water to the surface of the skin and hair, as well as deliver hydration to the deeper layers. (And in case you haven’t heard: Hyaluronic acid can hold 1,000 times its own weight in water.) Chances are you rely on other humectants in hair care—ever tried a honey hair mask?—so consider hyaluronic acid another top choice to ramp up hydration. 

In fact, plenty of leave-ins, shampoos, and stylers include the ingredient in their formulas already—hyaluronic acid for hair is not a new concept. But from this TikTok experiment, it seems using a proper skin care serum can be just as effective, if you can spare a few drops. 

“HA lives in my shower for the face and hair,” says board-certified internal medicine physician and skin care expert Zion Ko Lamm, M.D., in a duet video. If you have dry, frizzy, brittle, or damaged locks, she considers it a worthy addition to your routine (she typically uses it as a pre-shampoo or leave-in treatment). Best part? Like Lamm, you can streamline your routine and keep one vial on-hand for your skin and hair—both will drink the HA right up. 

The only caveat to note is that hyaluronic acid doesn’t exactly seal moisture into the strand. It helps draw in moisture from the environment, yes, but as Lamm says: “It does not take the place of hair oils.” You’ll still want to lock in all that water with an occlusive product, or the precious hydration can seep out, and your hair may become even more limp and dry than before. 

Mandelic acid is a member of the AHA family, which means its main gig is to exfoliate, brighten, and stimulate cell turnover. Like other AHAs, it’s derived from plants—in mandelic’s case, bitter almonds—and it hydrates the skin while sloughing off dead cells. As board-certified dermatologist Mona Gohara, M.D., tells us about the acid family: “They can be simultaneously exfoliating and hydrating, making them very beneficial to many skin types.” 

Some AHAs can be more intense than others—glycolic acid, for example, has the smallest molecular weight of the bunch, which means it can penetrate the skin’s outer layer quite easily. Mandelic acid, on the other hand, is larger in molecular size (even larger than lactic acid!), which may make it more tolerable for easily irritated skin types.

“It’s my absolute favorite AHA—way underrated in my opinion—as it is the most gentle,” says board-certified dermatologist Roberta Del Campo, M.D. “Meaning, anyone can use it, but it is just as effective as other AHAs, such as lactic acid and glycolic acid.”

When discussing dewy, hydrated skin, hyaluronic acid tends to creep up in conversation. It’s the key molecule involved in skin moisture, after all, and 50% of the body’s total amount of hyaluronic acid resides in the skin. And, of course, there’s the famous factoid that hyaluronic acid can hold 1,000 times its own weight in water: It’s referenced so much in skin care, we might as well slap the slogan on a T-shirt and send it out to the fanbase. 

Hyaluronic acid is a fabulous hydrator, so it definitely deserves all the hype: “It draws water into the stratum corneum, the top layer of the skin. It is a humectant, so it gives an immediate improvement in the way the skin looks—less ashy, dry, dull,” holistic dermatologist Cybele Fishman M.D., told us about the beloved ingredient. 

In the hopes of softer, plumper, more elastic skin, many flock to HA-infused serums—and because you can find an overwhelming number of these on the market, here we’ve rounded up the very best. 

A quick note: On the hunt for the best hyaluronic acid serum, chances are you’ll come across some funky names, like sodium hyaluronate, sodium acetylated hyaluronate, and hydrolyzed hyaluronic acid. Don’t sweat the science jargon: All “hydrolyzed” means is breaking the chemical down with water so it’s easier for your skin to absorb (regular HA has a larger molecular weight, which can make it difficult to penetrate into pores). Sodium hyaluronate, a salt-form of hyaluronic acid, has an even smaller molecular weight than hydrolyzed HA, so it can really shimmy into the deep layers of your skin. 

But enough chemistry—let’s dive into our all-time favorite hydrators. 

According to the study, “rumination syndrome involves effortless, repeated regurgitation, and can overlap with other upper gastrointestinal (GI) disorders, including gastroparesis.” 

It occurs when patients spit up their food about 10 minutes after they’ve swallowed it. This is different from vomit since the food has not been fully digested. 

Rumination is considered a disorder of the gut-brain interaction (DGBI), making it a learned response. While it’s not entirely clear why it happens, researchers suggest it’s a response to pain or discomfort in the stomach. 

Because it’s similar to the act of vomiting, many patients unknowingly describe their symptoms as vomit or reflux. Other symptoms, like feeling full quickly, tightness in the abdomen, nausea, and unwanted or unintentional weight loss, are similar to symptoms of stomach pain, indigestion, and gastroparesis. This can cause the disorder to go undiagnosed or misdiagnosed for long periods of time, the researchers say. 

To better understand the syndrome, researchers looked at 242 patients with gastrointestinal symptoms similar to rumination. Of those volunteers, more than 12% qualified for a rumination diagnosis, and nearly half of that group said the condition impacted their social lives. 

“This condition causes a lot of embarrassment and may stop people from eating with others,” co-author of the study, Trisha Satya Pasricha, M.D., says in a news release. “It is not well understood, and is often mistaken for other disorders.”