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Cottage cheese. Chicken breast. Khloe’s Kardashian’s (predictably-named) Khloud white cheddar popcorn. What do all three of these items have in common? They’re all sources of protein (though you won’t find that last one on the food pyramid).
Biologically-speaking, protein (which is made up of structural units called amino acids) plays an enormously large role in the function of the human body. And while the macronutrient is popularly discussed in conversations surrounding muscle gain and satiating hunger, how much (or little) of it you’re consuming can also impact the health and structure of your skin, hair, and nails.
“If you're not eating enough protein, your body starts prioritizing—vital organs get first dibs, and skin, hair, and nails get what’s left,” says Mona Gohara, MD, a board-certified dermatologist and associate clinical professor at Yale School of Medicine. “Since keratin, collagen, and other skin-supportive proteins are made from amino acids, your diet is basically the supply chain. If it’s broken or understocked, production slows.”
Therefore not consuming enough protein can lead to a slew of less-than-desirable side effects like brittle nails, thinning hair, dry, flaky skin, and even a loss of skin elasticity. (A quick note: The health consequences of not consuming enough protein can be much more serious than weakened fingernails, which is why protein is considered a dietary essential—more on that below).
Ahead, experts break down how protein is involved in the formation of your hair, nails, and skin, what happens when you don’t eat enough, how the damage can be undone, and why topical beauty products aren’t the answer to the problem.
What is protein?
According to Dr. Gohara, you can think of protein as being both the construction crew and the scaffolding of your entire body. “Protein is like the building material your body uses to construct everything from muscle and bone to skin, hair, and nails,” she says.
Heather Woolery-Lloyd, MD, a board-certified dermatologist based in Miami, says proteins are important for nearly every process in the body—which may help you understand why they’re typically described as being the “building blocks” of life. Not only do proteins construct and repair all of the body’s tissues, but they also drive chemical reactions, transport substances throughout the body, and form the immune system, she says. “Without sufficient protein, your body can't build or maintain itself, fight off illness effectively, or perform its essential functions,” Dr. Woolery-Lloyd explains.
Breaking it down a little further, proteins are made up of their own building blocks or repeating units called amino acids. “These amino acids function as molecular building blocks that the body assembles into various proteins required for cellular repair, enzyme production, and tissue maintenance,” explains Pooja Rambhia, MD, a board-certified dermatologist based in New York City. The body is not capable of making all of the amino acids you need to function, which is why you must get them from your diet. Once you consume protein, your body breaks it down and uses the amino acids where they are needed. And as Dr. Gohara said, enhancing your hair, skin, and nails understandably comes second to, say, producing antibodies.
How is protein involved in the formation of your hair, skin, and nails?
Still, skin, hair, and nails would be nonexistent without protein. The three key proteins involved in the structure of skin are collagen, elastin, and keratin. According to Dr. Gohara, collagen gives structural support and firmness to the skin, while elastin provides elasticity—meaning it allows skin to stretch and bounce back to its original shape. As we age, our bodies produce less of these proteins, leading to the formation of wrinkles and skin laxity. (So when a skin-care product claims to boost collagen production, it’s inferring it helps ward off the formation of wrinkles or simply reduce the appearance of them.)
Both collagen and elastin are produced by skin cells called fibroblasts in the dermis, the second layer of the skin. The outermost layer of skin, known as the epidermis, is made up of a fibrous protein called keratin, which is produced by skin cells called keratinocytes, Dr. Gohara explains. “As keratinocytes move upward through the layers of skin, they produce more keratin, eventually forming a strong, protective barrier,” she says.
Keratin is also the key protein involved in the formation of your nails. “Nails are composed almost entirely of keratin proteins that have been hardened and compacted into layers, giving them their characteristic strength and durability,” says Dr. Rambhia. While keratin is really the main component of nails. Dr. Gohara says that collagen and elastin play an additional role in nail structure by supporting the nail matrix, the skin where fingernail and toenail growth occurs.
When it comes to the structure of hair, keratin is also the main character, but there are other proteins (supporting characters, if you will) called keratin-associated proteins that support the cause. According to Dr. Woolery-Lloyd, you can envision human hair as a rope. “The main strands of that rope are made of keratin, but to make that rope extra strong and prevent it from unraveling, you need something to bind those strands together. That's where keratin-associated proteins (KAPs) come in,” she says.
KAPs create strong connections between strands of keratin, Dr. Woolery-Lloyd explains. “This cross-linking forms a really dense network, which is what gives hair its strength, shape, and resistance to damage. While keratin provides the core structure, KAPs are essential for reinforcing the hair shaft,” she adds.
Both the hair and the nails require additional proteins, like enzymes and transport proteins, to support growth and development, adds Dr. Rambhia.
How is it different from the protein required from the rest of your body?
“Keratin and other structural proteins in hair and nails differ from most functional proteins in the body in terms of composition, structure, and role,” explains Dr. Rambhia.
For instance, she says keratin is rich in an amino acid called cysteine, which is responsible for forming strong chemical bonds called disulfide bonds. “This gives keratin its exceptional strength and resistance to degradation,” she says. For reference, some bond-building hair-care products work to repair or strengthen these bonds, which are broken when hair is severely damaged during chemical treatments. Another key characteristic of keratin? It’s water resistant, thanks to its concentration of hydrophobic (aka, water-repelling) amino acids.
“Unlike metabolically active proteins such as enzymes and hormones—which are regularly synthesized and broken down—keratin is biologically stable and persists for long periods,” Dr. Rambhia says.
Melanie Palm, MD, a board-certified dermatologist, says that keratin and KAPs’ slow turnover and high cross-linking (chemical bridges that bind to protein chains) make them exceptionally resilient structures, especially compared with other proteins in the body that are sensitive to environmental changes and are rapidly recycled.
“This unique composition is what allows hair and nails to maintain their structure and integrity over time,” she says.
What happens to your hair, skin, and nails when you don’t eat enough protein?
Protein deficiency can manifest in your skin, hair, and nails in several different ways. Your nails may become brittle and may be more prone to splitting, peeling, and breaking, says Dr. Rambhia. “Nails may also develop horizontal ridges called Beau’s lines, which reflect temporary disruptions in nail growth,” she adds. (But Dr. Rambhia says these can also be caused by certain medications and medical conditions like uncontrolled diabetes and pneumonia, among others, so consult with a board-certified dermatologist.)
Hair takes a hit in the form of dullness, thinning, shedding, and increased breakage. In severe cases, hair growth can slow or completely halt. Symptoms of severe protein deficiency can show up in the skin as well. In these instances, Dr. Gohara says the skin may peel, flake, and bruise more easily, and wounds can take longer to heal. Experts say severe protein deficiency can do far more damage than meddling with your nails, hair, and skin. In prolonged cases, Dr. Rambhia says it can contribute to progressive muscle mass loss and immunocompromisation, among other medical conditions that require immediate medical intervention.
That all said, experts say protein deficiency isn’t a particularly common condition in the United States. “In patients who are otherwise healthy and eating a balanced diet, it’s relatively uncommon to see clear signs of protein deficiency just through hair and nails,” says Dr. Rambhia. “That said, in individuals with restrictive diets, chronic illnesses, or absorption issues, the body may prioritize essential organs over skin, hair, and nails, leading to visible changes like brittle nails, slow nail growth, or thinning hair,” she further explains.
These symptoms can also be caused by other health conditions. For instance, Dr. Palm says there are a multitude of autoimmune conditions—like Grave’s thyroiditis, Hashimoto’s thyroiditis, and lupus, for example—that may cause similar symptoms to be present.
And while protein is certainly irreplaceable when it comes to overall skin, hair, and nail health, Lauren Manaker, a registered dietitian, says all three are influenced by other factors, like hydration, genetics, and other vitamins and minerals. “Protein lays the foundation, but it's only one piece of the puzzle,” she says.
Can the damage be fixed?
For starters, if you’re noticing symptoms like brittle nails and thinning hair, Dr. Gohara recommends bringing it up to your doctor to determine if the root cause is nutritional or another underlying health issue. If your hair and nail symptoms are determined to be due to a protein deficiency, Dr. Gohara says working with a healthcare provider or a registered dietitian to address the issue and create a game plan is key.
Eating more protein can help, but the exact amount needed to reverse the damage depends on the individual. And even when you’re eating the recommended portion, it'll take some time for the damage to improve. You’re certainly not going to see miraculous results after making yourself a week of salmon dinners.
Since nails only grow about two to three millimeters per month, Dr. Rambhia says it could take between three and six months for stronger, healthier nails to grow, while visible improvement in hair thickness and strength can take between three and six months. Depending on the length of your hair, it may take over a year for all the damage to grow out, she adds. For skin, visible improvement may take weeks or months, depending on the severity of the protein deficiency. “The healing process is influenced by multiple variables including baseline health status, age, degree of protein depletion, and adherence to nutritional rehabilitation,” says Dr. Rambhia. “Good nutritional status is essential for wound healing to take place, and ignoring nutritional status may compromise the patient’s ability to heal and subsequently prolong the stages of wound healing.” However, Dr. Rambhia adds that addressing the issue early on with adequate protein intake typically results in a faster and a more complete recovery of skin appearance and integrity.
According to Manaker, the general recommendation for protein intake for most adults is around 0.8 grams of protein per kilogram of body weight per day, though this can vary depending on the individual and their specific health concerns or fitness goals—and in an ideal world, this total should be split between all of your daily meals.
To put that into perspective, Manaker says one large egg has about six grams of protein, a three-ounce serving of shrimp yields 20 grams of protein, and three ounces of grilled chicken breast totals in at 26 grams of protein. An eight-ounce glass of ultra-filtered milk comes in at 13 grams of protein. (For those that are lactose-free, Manaker says that lactose-free milk provides the same nutrients just without the lactose sugar.)
“The [daily protein] recommendation is based on what most bodies need to maintain their basic functions, including repairing tissues, supporting immune health, and producing important substances like keratin,” says Manaker. “Beyond just nails and hair, it ensures all your body’s systems work properly.”
She adds that vegan eaters can easily hit their protein goals with a little planning, and that leaning on soy foods, seeds, nuts, and certain grains like quinoa can provide a boost in the nutrient. Some other examples of plant-based protein include lentils, chickpeas, and tofu.
All forms of protein-rich food can help support nail, skin, and hair health by providing amino acids, but there are some that are particularly beneficial for these areas, Manaker explains. For example, she says eggs and fish, rich in biotin, can help support keratin production.
While eating more than the generally-recommended amount of protein may be beneficial for those looking to make muscle gains, it’s not going to do your hair, nails, and skin any special favors.
“The truth is, your body can only use so much, and hair and nail health are influenced by a variety of factors, not just protein,” says Manaker. “Once your body has enough protein to support hair and skin health, there doesn't appear to be any additional benefit to overconsumption when it comes to hair and nail health,” she adds.
In fact, according to Dr. Gohara, once your body’s protein needs are met, the excess is stored as fat or excreted. “In people with normal kidney function, moderate increases aren’t harmful, but megadosing won’t supercharge your shine,” she says.
Can topical hair and nail-care products repair the damage?
If your nails are breaking because your diet is majorly lacking protein, painting on a nail-strengthening polish can offer short-term benefits, but it won’t actually cure the problem. The same goes for applying a keratin-infused hair-care treatment advertised to strengthen strands, smooth flyaways, and ward off breakage. According to Dr. Palm, these products may improve surface systems (like temporarily strengthening the outer layers of nails and hair), but they don’t address the biological causes (in this case, perhaps nutritional deficiencies) affecting nail and hair health.
Another way to think about it: Topical beauty products formulated with protein (like a keratin-infused hair mask) cannot replenish your body’s protein reserves. That’s because visible hair and nails are composed of dead cells, so they can’t absorb or use protein like living tissues can, says Dr. Rambhia. Yep, you read that right: All the effort we expend on our hair and nails is actually just us dressing up dead cells.
That’s not to say that hair and nail products are a total waste of time if you’re mending damage from a lack of dietary protein and want a quick cosmetic fix while you address the root cause. “Optimal results typically require a combination of external care and internal support through a balanced diet or targeted supplements like biotin, iron, or amino acids,” says Dr. Palm.
When shopping for nail-care products, Dr. Palm recommends looking for products with hydrating ingredients (like glycerin and urea), barrier-protecting ingredients (like ceramides), and strengthening ingredients (like keratin and calcium). “Cuticle oils with vitamin E or jojoba oil can also support nail health by nourishing the matrix,” she says.
As far as hair-care products go, Dr. Palm suggests products with ingredients like silk proteins, peptides, and hydrolyzed keratin to help repair and emollients like argan oil and glycerin to supply moisture and boost shine. “Scalp-supportive actives such as caffeine or rosemary oil may improve circulation and promote a healthier environment for growth,” she adds.
Ultimately, dietary protein really is an important player in the function of your entire body, and your skin, nails, and hair benefit from it making your plate in recommended amounts. Whether or not protein-coated popcorn really needs a place in your pantry? Well, that’s up to you.