Your skin is nourished through a combination of internal blood supply, oil glands, water channels, and the nutrients you eat. Unlike most organs, the outermost layer of skin has no blood vessels at all, so it depends on an elegant relay system to receive everything it needs. Understanding how this works explains why certain habits, foods, and products actually make a difference in skin health.
How Nutrients Reach the Surface
Skin has two main layers: the dermis (deeper) and the epidermis (outer). The dermis is rich with tiny blood vessels called capillaries, which deliver oxygen, glucose, amino acids, vitamins, and minerals directly to dermal cells. The epidermis, however, contains no blood vessels whatsoever. Every nutrient it receives must travel upward from capillaries in the dermis.
Between these two layers sits a thin, nanoporous membrane called the dermal-epidermal junction. This membrane acts as a selective filter, allowing small molecules like vitamins, sugars, and dissolved minerals to pass through while blocking larger molecules and cells. The junction isn’t flat. It has a wavy, interlocking shape that increases the contact area between the two layers, maximizing the surface available for nutrient exchange. As skin ages, this junction flattens, shrinking that contact area. The result is weaker nutrient and oxygen exchange, which contributes to the thinning and fragility of older skin.
Water Channels That Keep Skin Hydrated
Water doesn’t just soak into skin cells passively. Specialized protein channels embedded in cell membranes actively shuttle water and glycerol into the epidermis. These channels play a key role in maintaining hydration in the outermost layer of skin, which is the layer most exposed to the environment and most prone to drying out.
Glycerol turns out to be especially important. In studies where these water channels were impaired, skin didn’t just lose water. It lost glycerol, and that glycerol loss was the real driver of dryness. Replacing glycerol (topically, orally, or by injection) corrected the hydration problem, while other moisturizing agents like urea or xylitol did not. Epidermal glycerol levels directly correlate with how well the outer skin layer holds onto water.
The Skin’s Built-In Moisturizing System
Your outermost skin cells contain a mixture of compounds collectively called natural moisturizing factor, or NMF. This isn’t a single substance but a blend of free amino acids, lactic acid, urea, sugars, and inorganic salts including sodium, potassium, calcium, and magnesium in the form of chlorides, phosphates, and citrates. NMF also includes a natural UV-absorbing compound called urocanic acid.
These molecules are hygroscopic, meaning they pull water from the surrounding environment and hold it inside the outermost skin cells. When NMF levels drop (from harsh cleansers, dry climates, or aging), skin feels tight, rough, and flaky. Many effective moisturizers work by replenishing one or more NMF components rather than just coating the surface.
How Sebum Protects the Surface
Sebaceous glands in the dermis produce an oily substance called sebum that coats the skin’s surface. Human sebum is a specific mix: roughly 57.5% fatty acids and triglycerides, 26% wax esters, and 12% squalene, with smaller amounts of cholesterol. Two of these components, squalene and wax esters, are found nowhere else in the body. They exist only in sebum and serve as a primary protective coating for the skin surface.
This oil layer does several things at once. It slows water loss from the epidermis, keeps the skin surface slightly acidic (which discourages harmful bacteria), and provides a layer of lubrication that prevents cracking. People who produce too little sebum tend to have dry, easily irritated skin. People who produce too much are prone to acne, but the sebum itself is a nourishing and protective system when balanced.
Key Vitamins for Skin Health
Vitamin C is one of the most important nutrients for skin. It serves two distinct roles: it’s a potent antioxidant that neutralizes free radicals caused by UV exposure, and it’s essential for collagen production. Without adequate vitamin C, the body cannot properly stabilize collagen molecules, which provide the structural support that keeps skin firm. Vitamin C also stabilizes collagen’s genetic instructions inside cells, increasing the amount of collagen protein produced for skin repair.
Vitamin E works alongside vitamin C in antioxidant defense. On its own, vitamin C provides limited protection against UV damage. But when combined with vitamin E (either through diet or topical application), the two vitamins together significantly increase the skin’s resistance to sunburn and reduce blood flow to UV-damaged areas. Topical formulations containing both vitamins are more effective at preventing sun damage than either one alone.
Dietary Fats and the Skin Barrier
The outermost layer of your epidermis is held together by a lipid (fat) barrier composed of roughly 50% ceramides, 25% cholesterol, and 10 to 20% free fatty acids. When this ratio is disrupted, the barrier weakens, leading to dryness, irritation, and increased sensitivity. Omega-3 and omega-6 fatty acids from your diet directly influence this barrier’s integrity.
Omega-3 fatty acids (found in fatty fish, flaxseed, and walnuts) reduce skin inflammation and can increase the production of filaggrin, a protein critical for barrier function and moisture retention. EPA, one specific omega-3, has been shown to influence ceramide levels in skin. A higher ratio of omega-3 to omega-6 in your diet generally favors better barrier function.
Certain omega-6 fatty acids also help. Gamma-linolenic acid, found in evening primrose oil and borage oil, has anti-inflammatory properties and is linked to increased ceramide production. Studies suggest that consuming oils rich in these fatty acids can measurably improve skin barrier function, particularly in people whose baseline levels are low.
What Topical Products Can Actually Deliver
Not everything you put on your skin can actually get in. The outermost layer of skin, the stratum corneum, is a remarkably effective barrier. A widely cited principle in dermatology holds that only molecules under 500 Daltons (a unit of molecular weight) can penetrate this layer. For reference, most common topical medications, contact allergens, and active skincare ingredients all fall below this threshold.
This is why collagen in a face cream, for instance, cannot penetrate into your skin. Collagen molecules are far too large. But smaller molecules like vitamin C (in certain forms), retinol, niacinamide, and glycerol pass through readily. When choosing topical products, the active ingredient’s molecular size matters more than its concentration on the label.
How Exercise Feeds Your Skin
Physical activity is one of the most effective ways to increase nutrient delivery to skin. During exercise, your body temperature rises and blood vessels in the skin dilate to release heat. This process can double skin blood flow overall, and during intense exercise, blood perfusion in the skin increases roughly eightfold.
That surge of blood carries more oxygen, glucose, and micronutrients to the dermis, where they can diffuse up into the epidermis. It also accelerates the removal of metabolic waste products from skin tissue. Regular exercise doesn’t just boost circulation during a workout. It improves the skin’s vasodilatory function over time, meaning the blood vessels in your skin become more responsive and efficient at delivering nutrients even at rest. Exercise also supports skin cell metabolism, regulates stress hormones that can worsen inflammatory skin conditions, and promotes the production of anti-inflammatory compounds.