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Your skin has three layers, each with its own job
The epidermis renews itself about once a month
Your skin is also a vitamin D factory
The dermis holds collagen, elastin and the skin's supply lines
The hypodermis is a built-in cushion and fuel tank
How food becomes skin, layer by layer
Smart use of supplements for skin structure
The bottom line

Key takeaways

Your skin weighs about six pounds and is only about 2 millimeters thick on average, yet it holds three distinct layers with very different jobs¹.
The outer layer (epidermis) renews itself about every 28 to 30 days in young adults, and the cycle stretches to about 45 to 50 days in older adults².
The middle layer (dermis) makes up about 90 percent of your skin’s thickness, and collagen accounts for nearly three quarters of its weight²³.
Blood vessels in the dermis carry nutrients to every layer of skin, so what you eat and drink becomes the raw material for your skin³.
In a national survey of women ages 40 to 74, those who ate more vitamin C or more linoleic acid were less likely to have dry skin⁴⁵⁶.

Right now you are wearing about six pounds of living tissue. On average it is about 2 millimeters thick, close to the thickness of a nickel, and it wraps every inch of you¹. It is your skin, the largest organ in your body¹.

That thin covering does a remarkable amount of work. It helps control your body temperature, gathers information about the world around you, and stores water, fat and vitamin D¹. It is made of water, protein, fats and minerals⁷. Every one of those raw materials comes from what you eat and drink.

This guide takes you on a tour from the surface down. At each stop you will meet the cells that live there, learn what they do, and see which nutrients supply their building blocks.

Your skin has three layers, each with its own job

Think of your skin as a three-story building. The top floor is the epidermis, a thin and tough outer layer. The middle floor is the dermis, a thicker layer of connective tissue. The ground floor is a fatty layer called the subcutis or hypodermis¹.

The three layers differ in function, thickness and strength¹. The epidermis faces the outside world and keeps renewing itself. The dermis gives skin its strength and stretch, and it holds the blood vessels, nerves and glands. The hypodermis cushions you, keeps you warm and stores energy²⁷.

Thickness changes a lot from place to place. The epidermis is only about 0.05 millimeters thick on your eyelids, but it reaches about 1.5 millimeters on your palms and the soles of your feet². The dermis is the thickest of the three layers, making up about 90 percent of the skin’s thickness²⁷.

One fact shapes everything about feeding your skin. The epidermis has no blood vessels of its own³. Instead, blood vessels in the dermis supply nutrients for all the skin layers, and the outer cells receive them by slow seepage (diffusion) from below³⁸. The vitamin C in your morning orange travels through your bloodstream into the dermis and then works its way up toward the surface.

The epidermis renews itself about once a month

The epidermis is made of five sublayers that work together to keep your surface fresh². From the bottom up, they are the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum and stratum corneum⁹. The stratum lucidum shows up only in thick skin, such as the palms and soles¹⁰.

The cell that does most of the work here is the keratinocyte. Keratinocytes make up about 90 to 95 percent of the cells in the epidermis³. They produce keratin, a tough protective protein that forms most of your skin, hair and nails².

New keratinocytes are born in the deepest sublayer, the basal layer. These cells divide again and again, and the new cells constantly push older ones up toward the surface². On the way up, they fill with keratin, and by the time they reach the top they are no longer alive. There they form the stratum corneum, 10 to 30 thin layers of dead cells that are steadily shed².

How long does the whole trip take? According to the National Cancer Institute, complete turnover takes about 28 to 30 days in young adults and about 45 to 50 days in older adults². The Cleveland Clinic puts it simply: you have new skin about every 30 days⁷. Researchers at Oregon State University’s Linus Pauling Institute note that keratinocytes in older skin are slower to mature and shed³. The bigger picture of how skin changes over the decades is covered in our article on skin aging.

Several specialized cells share the epidermis with the keratinocytes. Melanocytes sit in the basal layer and make melanin, the pigment that gives skin its tan or brown color². Melanin also shields the deeper layers from the sun². A single inch of skin holds roughly 19 million skin cells and about 60,000 melanocytes⁷.

Langerhans cells serve as the skin’s first-line immune defenders¹⁰. They latch on to invaders that slip into damaged skin and alert the rest of the immune system². Merkel cells, found in the basal layer, help you sense touch²¹⁰.

The stratum corneum is where your body meets the world. Its flat, dead cells and the fats packed between them form the skin barrier, which holds water in and keeps irritants out⁶. That barrier has its own article in this library, and so does skin hydration, the science of how much water your skin holds.

Your skin is also a vitamin D factory

Your skin does a job that surprises many people: it makes vitamin D. When ultraviolet B (UVB) light from the sun reaches the epidermis, it turns a cholesterol-like compound called 7-dehydrocholesterol into vitamin D3¹¹. This happens mainly in keratinocytes of the two deepest sublayers, the stratum basale and stratum spinosum¹¹.

Several things change how much vitamin D your skin can make. Melanin competes for UV light, so people with darker skin may need up to 10 times as long in the sun to make the same amount¹¹. Older skin makes less, because it holds less of the starting compound¹¹. Season matters too. At about 40 degrees north latitude, near Philadelphia, Columbus and Denver, winter sunlight carries too little UVB to make vitamin D¹¹. That stretch runs from November through early March¹¹.

Vitamin D also helps run the skin itself. Its active form switches on genes that help keratinocytes mature¹¹. That maturing process supports normal cell growth, recovery from small injuries and the skin barrier¹¹. Vitamin D also helps regulate cathelicidin, a natural antimicrobial protein that supports the skin’s defenses¹¹.

Winter sun, skin tone and age all shape what your skin can produce. That is why many people get part of their vitamin D from food and supplements. Your healthcare team can check your blood level and help you choose an amount that fits you. Sun exposure itself is covered in our article on UV exposure.

The dermis holds collagen, elastin and the skin’s supply lines

Below the epidermis lies the dermis, the thickest and busiest layer. It ranges from about 0.6 millimeters on your eyelids to about 4 millimeters on your back¹². It has two parts. The upper papillary layer holds a thin web of collagen fibers, tiny capillary loops and builder cells called fibroblasts²¹². The deeper reticular layer is made of thick collagen fibers that run parallel to the skin’s surface².

Fibroblasts are the construction crew. They are the most common cells in the dermis, and they make structural proteins such as collagen³. Their output is impressive: nearly 75 percent of the dermis, by weight, is a mesh of collagen³. Collagen is also the most abundant protein in your whole body. It accounts for about 30 percent of your total protein, and one form, type I collagen, makes up 90 percent of your body’s collagen¹³.

Woven through the collagen are elastic fibers made of elastin. Elastin is the protein that lets your skin spring back into place after it stretches². Collagen gives skin its strength, while elastin gives it bounce.

The dermis also houses much of your skin’s equipment. Blood vessels deliver oxygen and nutrients, and lymph vessels carry immune cells². Nerve endings let you feel pressure, pain, heat, cold and itch¹². You have about 3 million sweat glands, and together they can release up to 2 liters of sweat an hour to cool you down². Oil glands (sebaceous glands) release sebum, an oily lubricant, and hair follicles grow hair across most of your skin¹².

Those oil glands have a surprising nutrition link. Vitamin E is the most abundant fat-soluble antioxidant in human skin¹⁴. It collects first in the sebaceous glands and then travels to the skin’s surface in sebum¹⁴. When you take in vitamin E by mouth, it takes at least seven days for the amount in your sebum to change¹⁴.

Collagen production shifts over time. Your body makes less collagen as you age, and existing collagen breaks down faster¹³. That change is a big part of the skin aging story, which has its own article in this library.

The hypodermis is a built-in cushion and fuel tank

The deepest layer goes by several names: hypodermis, subcutis or subcutaneous tissue. It is made of a network of fat cells and collagen².

This layer does quiet but important work. It insulates your body, which helps you hold on to heat². It absorbs shocks, so it protects your muscles, bones and inner organs when you bump into something or fall²⁷. Its fat cells also provide structural support and act as an energy reserve your body can draw on³.

The thickness of the hypodermis varies across the body and from person to person². Because it is mostly stored fat, this layer reflects your overall eating pattern and activity rather than any single vitamin. Balanced meals with healthy fats are its best everyday support.

How food becomes skin, layer by layer

Because the dermis feeds every layer, the nutrients you eat really do reach your skin. One trial shows how directly. In it, 42 adults took 4 grams a day of EPA, an omega-3 fat from fish oil, for three months. The EPA content of their skin rose about eightfold⁶. Vitamin C behaves in a similar way. Skin levels appear to rise as blood levels rise⁸. In two studies, people who took vitamin C as a supplement had more of it in their skin afterward⁸.

Here is how the main nutrients map onto the layers.

Vitamin C helps build collagen

Vitamin C is a required helper (cofactor) for the enzymes that stabilize the structure of each collagen molecule⁸¹⁵. It also prompts fibroblasts to make more of the genetic messages (mRNA) used to build collagen⁸. Up in the epidermis, vitamin C supports the making and organizing of barrier fats⁸. The epidermis typically holds 2 to 5 times more vitamin C than the dermis⁸.

Zinc supports new cell growth

About 6 percent of your body’s zinc is found in your skin¹⁶. The epidermis holds about five times more zinc than the dermis¹⁶. Zinc takes part in the division and maturing of basal cells¹⁶. It is also part of several skin enzymes, including the antioxidant enzyme superoxide dismutase¹⁶. Along with vitamin C, copper and manganese, zinc is one of the nutrients your body needs to assemble collagen¹³.

Vitamin A guides growing cells

Your skin converts vitamin A into retinoic acid, which adjusts gene activity in both the epidermis and the dermis¹⁷. Skin cells can also turn beta-carotene, the orange pigment in carrots and sweet potatoes, into vitamin A compounds¹⁷. In rats, a shortage of vitamin A led to abnormal hardening of the skin’s surface tissue¹⁷. Their sweat and oil glands also wasted away¹⁷.

Essential fatty acids supply the surface

Linoleic acid is an omega-6 fat found in plant oils, nuts and seeds. Your skin builds it directly into special fats called ceramides in the stratum corneum⁶. Ceramides make up 40 to 50 percent of the fats in that top layer⁶. The more linoleic acid they carry, the better the barrier tends to work⁶. When people fall short on essential fatty acids, their skin turns dry and scaly and loses more water⁶.

Protein supplies the raw material

Collagen is rich in three amino acids: proline, glycine and hydroxyproline¹³. Your body cannot absorb collagen whole, so it breaks dietary collagen down into smaller pieces first¹³. What matters is a steady supply of the raw ingredients. Fish, egg whites, meat, peanuts and mushrooms provide proline, and poultry, red meat and peanuts provide glycine¹³.

What a large survey found

These lab findings line up with what researchers see in everyday diets. One study looked at women ages 40 to 74 from the first National Health and Nutrition Examination Survey (NHANES I)⁴⁶. Researchers compared what the women ate with the results of their skin exams⁴⁶. Women who ate more vitamin C had better skin appearance, with fewer wrinkles, and were less likely to have dry skin⁵. Women who ate more linoleic acid were less likely to have dry or thinning skin⁶. A survey like this shows a link rather than cause and effect, and it fits well with the lab research on how these nutrients work.

Layer	What it does	Main building blocks	Nutrients that support it
Stratum corneum (top of epidermis)	Forms the barrier and sheds old cells	Keratin, ceramides	Linoleic acid, vitamin E (via sebum), vitamin C
Living epidermis	Makes new cells, pigment and vitamin D; stands immune guard	Keratinocytes, melanocytes	Zinc, vitamin A, vitamin D, vitamin C
Dermis	Gives strength and stretch; holds vessels, nerves and glands	Collagen, elastin, fibroblasts	Vitamin C, protein, zinc, copper
Hypodermis	Cushions, insulates and stores energy	Fat cells, collagen	Balanced meals with healthy fats

Sources:^{23681113141617}

Smart use of supplements for skin structure

A colorful plate covers many of your skin’s needs, and supplements offer a convenient way to fill gaps. Several have been studied for their effects on skin.

Collagen peptides are one of the most popular choices. They are small pieces of collagen, sold as pills and powders and often labeled “hydrolyzed collagen”¹³. Your body absorbs them through the digestive tract as smaller peptides and amino acids¹³. The Cleveland Clinic describes collagen peptides as possibly effective for improving skin hydration and skin elasticity¹³. Results vary from study to study, and researchers are still working out the best forms and doses.

Plant oils rich in essential fatty acids have encouraging trials too. In a 12 week trial, 45 women took 2.2 grams a day of flaxseed oil or borage oil. Both groups saw better results than the placebo group on every skin measure tested⁶. In another 12 week trial of 40 adults, people taking 1.5 grams a day of evening primrose oil had better skin moisture, elasticity and firmness⁶. Their skin was also smoother than the placebo group’s⁶.

For everyday nutrients, the daily recommendations make a good starting point. The recommended amount of vitamin C is 75 milligrams a day for women and 90 for men, and people who smoke need an extra 35 milligrams¹⁵. For zinc, it is 8 milligrams a day for women and 11 for men¹⁸.

A few smart-use habits help you get the most from any skin routine. Keep total zinc from food and supplements at or under 40 milligrams a day unless your clinician advises more¹⁸. Over the long term, high zinc intake can leave you short on copper, another collagen helper¹³¹⁸. Keep vitamin A to standard amounts, such as those in a multivitamin, unless your clinician suggests otherwise. That matters most during pregnancy.

When you choose a product, look for a third-party quality seal such as USP Verified, NSF Certified for Sport or ConsumerLab approved. Then give your routine 8 to 12 weeks. The skin trials above ran 12 weeks, and your epidermis needs about a month to finish a single renewal cycle²⁶. Finally, share your full supplement list with your healthcare team so everything works together with any medicines you take.

The bottom line

Your skin is a three-story structure that renews its top floor about once a month. Each layer draws on what you eat. Protein supplies the amino acids for collagen, and vitamin C helps lock collagen into shape. Zinc and vitamin A guide new cells, while essential fatty acids help seal the surface.

A plate with colorful produce, quality protein and healthy fats covers the basics. Supplements such as vitamin C, zinc, plant oils and collagen peptides can add support, especially when your diet falls short. Give any new routine a couple of months, since your skin renews on a monthly cycle and the skin trials described here ran 12 weeks.

Sources

National Cancer Institute. Anatomy of the Skin. SEER Training Modules, National Cancer Institute. Accessed 2026. training.seer.cancer.gov
National Cancer Institute. Layers of the Skin. SEER Training Modules, National Cancer Institute. Accessed 2026. training.seer.cancer.gov
Michels AJ (reviewed by Draelos ZD). Skin Health. Micronutrient Information Center, Linus Pauling Institute, Oregon State University. 2011. lpi.oregonstate.edu
Cosgrove MC, Franco OH, Granger SP, Murray PG, Mayes AE. Dietary nutrient intakes and skin-aging appearance among middle-aged American women. American Journal of Clinical Nutrition. 2007. pubmed.ncbi.nlm.nih.gov
Michels AJ (reviewed by Draelos ZD). Vitamin C and Skin Health. Micronutrient Information Center, Linus Pauling Institute, Oregon State University. 2011. lpi.oregonstate.edu
Angelo G (reviewed by Pilkington S). Essential Fatty Acids and Skin Health. Micronutrient Information Center, Linus Pauling Institute, Oregon State University. 2012. lpi.oregonstate.edu
Cleveland Clinic. Skin: Layers, Structure and Function. Cleveland Clinic. 2021. my.clevelandclinic.org
Pullar JM, Carr AC, Vissers MCM. The Roles of Vitamin C in Skin Health. Nutrients. 2017. pmc.ncbi.nlm.nih.gov
Cleveland Clinic. Epidermis (Outer Layer of Skin): Layers, Function, Structure. Cleveland Clinic. 2021. my.clevelandclinic.org
Yousef H, Alhajj M, Fakoya AO, Sharma S. Anatomy, Skin (Integument), Epidermis. StatPearls, NCBI Bookshelf, National Library of Medicine. 2024. ncbi.nlm.nih.gov
Drake VJ (reviewed by Bikle DD). Vitamin D and Skin Health. Micronutrient Information Center, Linus Pauling Institute, Oregon State University. 2011. lpi.oregonstate.edu
Cleveland Clinic. Dermis (Middle Layer of Skin): Layers, Function and Structure. Cleveland Clinic. 2022. my.clevelandclinic.org
Cleveland Clinic. Collagen: What It Is, Types, Function and Benefits. Cleveland Clinic. 2022. my.clevelandclinic.org
Michels AJ (reviewed by Traber MG). Vitamin E and Skin Health. Micronutrient Information Center, Linus Pauling Institute, Oregon State University. 2012. lpi.oregonstate.edu
Linus Pauling Institute. Vitamin C. Micronutrient Information Center, Oregon State University. 2026 (last updated). lpi.oregonstate.edu
Angelo G (reviewed by Polefka T). Minerals and Skin Health. Micronutrient Information Center, Linus Pauling Institute, Oregon State University. 2013. lpi.oregonstate.edu
Angelo G (reviewed by Fisher G). Vitamin A and Skin Health. Micronutrient Information Center, Linus Pauling Institute, Oregon State University. 2012. lpi.oregonstate.edu
Higdon J, Drake VJ, Delage B (reviewed by Ho E). Zinc. Micronutrient Information Center, Linus Pauling Institute, Oregon State University. 2019. lpi.oregonstate.edu

This article is for general education and is not medical advice. Talk with your healthcare professional about your own health, especially before starting a new supplement if you are pregnant, nursing, taking medicine, or managing a health condition. Statements about dietary supplements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Reviewed October 2026.