Bougie skin care is a singular pleasure. Spreading a fancy peptide serum, for instance, on your regular-person face might be the highlight of your day—even when you’re not exactly sure what those fancy ingredients do.As one of those fancy ingredients, peptides tend to be in expensive products—even by high-end skin-care standards. So why do companies charge such a premium for peptide serums and creams? Are they really that good?It’s complicated. On the one hand, peptides are one of the few trendy ingredients that scientists and dermatologists agree can really do something to combat the signs of aging, like fine lines, wrinkles, and sagging skin. On the other, companies make lofty claims about their peptide-containing products that may or may not fully match up with what we know about them.What even is a peptide?Peptides are molecules made up of relatively short chains of amino acids. Although they have a variety of uses in biochemical processes, they’re most often called the building blocks of proteins because, well, they’re what proteins are made of. If you think of a single protein molecule as a completed Lego Millennium Falcon, peptides are the individual blocks, while amino acids are the actual plastic.In the context of skin care, proteins almost always refers to collagen, the protein that gives your skin its structure. As we get older, the collagen proteins in our skin break down, contributing to everything from wrinkles to a lack of elasticity. Most peptide-containing products aim to either increase the amount of collagen your cells produce or decrease the amount of it that gets broken down, with the ultimate goal being smoother, plumper, healthier skin.Different peptides have different functions—sort of.All peptide products aim to deliver similar benefits. “Basically, as we age, we’re hoping to keep our skin thick,” Mary L. Stevenson, M.D., assistant professor in the Ronald O. Perelman Department of Dermatology at NYU Langone Health, tells SELF, tells SELF. “To do this you need to clear away cellular debris and breakdown products [from collagen breakdown], and stimulate the production of more collagen.” Peptides can do both of those jobs, but individual peptides may do this in different ways.So the specific way a product works depends on the individual peptides it contains. But figuring out which peptides a product contains can be confusing. Some products with peptide right in the name don’t list specific peptides in the ingredients—like this extremely expensive Tata Harper cream, which contains “hydrolyzed avocado protein,” but nothing else even remotely peptide-adjacent. Other products that do contain peptides may list them simply as peptides or oligopeptides, often followed by a number. (By the way, the prefix oligo- literally means “few” and usually refers to peptides with 20 amino acids or fewer—which covers pretty much every peptide used in cosmetics.)You don’t need to memorize the names of every peptide you might see on an ingredients list, but knowing roughly which kinds are out there can be very helpful when choosing a product. Most literature reviews of the function and efficacy of cosmetic peptides recognize five different categories, based on how they’re proposed to work.Signaling peptidesBy far the most commonly used cosmetic peptides, products containing these ingredients claim to maximize the amount of collagen in your skin. “Signaling peptides have different ways of [doing this],” Noelani Gonzalez, M.D., director of cosmetic dermatology at Mount Sinai West, tells SELF. “Pro-collagen segments can actually stimulate collagen production, but they can also signal skin [cells] that enough collagen has been broken down,” thus preventing your body from breaking down any more.Whether they’re actually helping make more collagen or just helping the skin hold onto what you’ve got, it’s easy to see why signaling peptides are everywhere in skin care right now. There are a lot of them too. Here are just a few you might see on a label:Carnosine and N-acetylcarnosineTrifluoroacetyl tripeptide-2Most palmitoyl tripeptides and palmitoyl hexapeptidesMost tetrapeptides, including tetrapeptide-21 and tetrapeptide TKEKMost hexapeptides, including hexapeptide-11 and hexapeptide-14Carrier peptidesThese are probably the second most popular skin-care peptide. “Carrier peptides hook up to another ingredient to facilitate its delivery [to skin cells],” Dr. González explains. “The most common ingredient is copper, which helps with wound healing.” Most products simply list copper peptides on the ingredients, but some products also use manganese carrier peptides in the form of manganese tripeptide-1.Neurotransmitter inhibitor peptidesNeurotransmitter inhibitors, which are less common than signaling and carrier peptides are, may decrease the appearance of fine lines by blocking the release of acetylcholine—a neurotransmitter heavily involved in muscle contractions. Yes, these peptides are supposed to literally relax your facial muscles. These are the main peptides in this class:Acetylhexapeptide-3Pentapeptides, including pentapeptide-3 and pentapeptide-18Tripeptide-3Enzyme inhibitor peptidesLike neurotransmitter inhibitors, enzyme inhibitors interfere with the activity of chemicals involved in a specific aging-related process. In this case, they’re inhibiting enzymes that mediate the breakdown of collagen and other skin proteins. In theory, this helps stave off collagen loss. The most common types are soybean peptides, silk fibroin peptides, and rice peptides.Structural or keratin peptidesStructural peptides are unique in that they specifically target dehydration and dryness. They’re usually derived from keratin—a protein that gives hair and nails their structure, among other things—and seem to work by improving skin barrier function, allowing it retain more water and give the skin a plumper look. If you see these at all, they’ll likely be listed as keratin peptides, or maybe wool lipids, since sheep’s wool is the most common source of keratin in this case.There is research to back up (some of) the claims about peptides in skin-care products.Usually you’re lucky if you find a handful of tiny studies about a trendy skin-care ingredient. This is not the case with peptides, which have been studied for so long in so many different medical contexts that we actually know a good deal about how they work—just not always in the way you’d want.Most of the experimental data we have on peptides come from in vitro experiments, like cell cultures looking at the expression of certain proteins or studies done on artificial silicone skin. Often these studies don’t directly apply to cosmetics or skin care but are taken as evidence anyway.For example, copper peptides have in fact been shown to improve wound healing, which is partially why people started putting them in cosmetics. But, as Dr. González explains, those results may not transfer to skin-care benefits: “Wounded and healthy skin have different topographies, so we don’t know if [copper peptides] work the same on healthy skin,” she says. Several studies ended up finding that cosmetics containing copper peptides do promote smoother, healthier skin, but it’s still not clear if the same wound-healing mechanism is responsible for those results.There are some peer-reviewed studies that test the efficacy of peptide products on actual human skin, and the results suggest that peptides seem to actually work. However, these aren’t the huge, double-blind clinical studies we’d all love to see—and they’re usually carried out by skin-care and pharmaceutical companies. According to Dr. González, this in itself isn’t automatically concerning: “Skin-care companies do good studies sometimes,” she says, but the studies still aren’t usually large enough to draw any huge conclusions. (The largest study I encountered was this 93-person experiment from 2005. Most had 15 to 40 participants.)As with most skin-care products, the claims around peptide serums are not FDA-regulated.From a consumer perspective, the most important thing to understand about peptides is that they’re “cosmeceuticals.” This is not an FDA-regulated classification; it’s a marketing term that implies a cosmetic product has “medicinal or drug-like qualities.” (And those qualities may be used to justify higher prices.) But cosmeceuticals are not drugs—at least, not according the FDA.For context, this is the agency’s definition of a drug:“The FD&C Act defines drugs as those products that cure, treat, mitigate or prevent disease or that affect the structure or function of the human body. If a product makes such claims it will be regulated as a drug.”In other words, as long as they don’t claim to cure a disease or alter the structure of your skin, peptides aren’t subject to the same FDA regulations as, for example, retinoids, salicylic acid, or benzoyl peroxide. This also means that peptides haven’t been studied as extensively as drugs, SELF explained previously, so we don’t know as much about how they work.Usually when people hear “cosmetic regulations,” they immediately picture, like, an eyeshadow palette crammed with illegal or irritating ingredients. But contamination isn’t typically the issue with cosmeceuticals. Instead the problem is how they’re labeled. When you buy a product that contains an actual drug, the label must list its concentration and the specific form used in the product. The same is not true of cosmetics—and therefore cosmeceuticals—no matter how scientific sounding the product or its claims are. There’s generally no way to know the concentration of peptides in a moisturizer, and in some cases it might not even be obvious which ones are in there.Still, dermatologists love ’em.Given the amount of favorable evidence out there, it’s not surprising that both experts I talked to were pretty pro-peptides. “Having reviewed the literature, and also anecdotally in my own practice, I think they do promote thicker skin,” says Dr. Stevenson, who uses a peptide product in her routine. But she recognizes that peptide products are expensive and might not be as splurge-worthy as other options that definitely work: “Anyone who’s putting down a reasonable amount of money on [antiaging skin care] should prioritize lasers and neurotoxins (a.k.a., Botox)—and a good relationship with a dermatologist.”Okay, so peptide creams can’t match the wrinkle-busting power of Botox and lasers. But what about retinoids, the other gold standard in collagen regeneration?Here’s where it gets fuzzy. Although they seem to work in similar ways, we know way less about peptides than we do about retinoids, and there aren’t many studies comparing them directly. (One small study found copper peptides to be comparable to tretinoin.) Based on their experiences with patients, Dr. Stevenson and Dr. González agree that peptides seem to be less irritating than retinoids, which may make them a good antiaging choice for people with sensitive skin. But if you already use and get antiaging benefits from a retinoid, you don’t necessarily need to try peptides.If you want, though, you can use them at the same time. “There’s no issue using peptides and retinoids simultaneously,” Dr. Stevenson says. “Just be sure to introduce one product at a time: Use one for two weeks on its own, then introduce the other.”Overall, peptides are a surprisingly evidence-supported ingredient that could make a difference in your skin—they just shouldn’t be your only strategy for fighting the signs of aging. “Retinoids, AHAs, and sunscreen should be the bulk of your skincare go-tos because they’ve been thoroughly tested and used for years. We know they work.” Dr. González says. “But peptides are great little extras.”Here are a few excellent peptide serums and creams to get you started.If you’re ready to take the plunge on a peptide serum or cream, check out these products. These are all recommended by the experts we spoke to or meet their criteria for a peptide skin-care product worth trying, meaning it lists the actual peptides in the product and has them fairly high up in the ingredients list.