Proteins, vitamins and minerals in skin care: what can they do from the outside?

“Rich in vitamins.” “Packed with proteins.” “Mineral-infused.” Skin care labels borrow the language of nutrition, and it sounds sensible: if these things are good to eat, they must be good for your skin too. Sometimes that’s true. Often it isn’t, because your skin was built to keep things out. Here’s what gets in, what stays on top, and how to read those words when you shop.

Your skin is designed to keep things out

The outer layer of your skin, the stratum corneum, is a wall of flat dead cells held together by fats. Its job is to stop water leaving and everything else coming in. That’s good for staying alive and inconvenient for skin care.

Researchers have a rule of thumb for what gets through: molecules heavier than about 500 daltons usually don’t reach meaningful levels in the skin. (A dalton is the unit used for the weight of a molecule; water is 18 daltons.) The rule has exceptions, mainly for molecules that are partly oil-loving and can slip between the fats, but it explains a lot. Small molecules like vitamins can pass. Large ones like proteins generally can’t.

So the first question for any “rich in” claim isn’t whether the ingredient is good for you. It’s whether it can physically get where it needs to go.

Vitamin C: gets in, with conditions

Vitamin C (L-ascorbic acid) is a small molecule, and it does real things in skin. It’s needed by the enzymes that build collagen, it neutralizes free radicals (unstable molecules produced by sun and pollution that damage cells), and it slows the enzyme that makes pigment.

The catch is the formulation. L-ascorbic acid is water-loving and carries an electric charge, so it crosses the outer layer poorly unless the product is quite acidic, below a pH of 3.5. Concentrations of roughly 10 to 20% are where the research shows an effect; below about 8% there isn’t much, and above 20% there’s more irritation without more benefit. It also oxidizes easily, which is why vitamin C serums turn yellow or brown and lose their punch.

One more thing the research is clear about: eating more vitamin C doesn’t deliver much extra to your skin, because only a small fraction of what you swallow gets there. For skin effects, topical is the practical route.

Niacinamide: the well-behaved one

Niacinamide (also called nicotinamide) is a form of vitamin B3. It’s small, stable, not fussy about pH, and well tolerated at the concentrations used in products, typically 2 to 5%. That combination is rare, which is why it’s in so many moisturizers.

What does it do? In lab studies it increases the skin’s production of ceramides, the fats that hold the outer layer together, which helps the barrier hold water. In trials on people, a 5% niacinamide moisturizer reduced hyperpigmented patches over 4 to 8 weeks (2% didn’t reach significance), and 4% reduced fine wrinkles over 8 weeks compared with the same cream without it. Those are modest, gradual changes, but they’re measured ones. If a moisturizer lists niacinamide near the top of its ingredients, the claim has a leg to stand on.

Vitamin E: an antioxidant that gets used up

Vitamin E (tocopherol) is oil-soluble, so it settles happily into the fatty parts of the outer skin. Even low concentrations, around 0.1%, raise vitamin E levels in the skin. There it works as an antioxidant: in human studies it reduced fat oxidation on the skin surface and redness after ultraviolet exposure.

Two honest caveats. Much of the vitamin E you apply is destroyed by sunlight as it does its job, so it’s protective in the moment rather than a store you build up, and it works better paired with vitamin C. And the stable ester form used in many products, tocopheryl acetate, needs to be converted by living cells to become active, which the dead cells of the outer layer can’t do well. Some people also get allergic contact dermatitis (an itchy rash from an allergy to something touching the skin) from vitamin E products, so it isn’t automatically the “gentle” option.

Proteins: mostly a surface effect

Collagen, keratin, silk, milk and wheat proteins show up on labels as if they were building materials for your skin. From the outside, they aren’t. Whole proteins are thousands to hundreds of thousands of daltons, far past the 500-dalton threshold. Even hydrolyzed collagen, which is chopped into smaller pieces, is mostly still too large to cross intact skin.

That doesn’t make protein ingredients useless. On the surface they form a light film that holds water and makes skin feel smooth, which is a fair cosmetic effect. Some very short chains of amino acids called peptides are small enough to get in, and a few are joined to a fatty acid specifically to help them penetrate. The evidence for those is still developing and depends heavily on the exact peptide. But “contains collagen” does not mean “adds collagen to your skin”, and no cream has been shown to do that.

Minerals: a few real jobs, lots of marketing

Minerals are a mixed bag, so ask what job each one is doing.

• Zinc oxide and titanium dioxide are sunscreen filters and, in diaper creams, physical barriers. Those are real, well-established uses.
• Salts of the natural moisturizing factor, like sodium PCA and sodium lactate, help the outer layer hold water.
• “Mineral-rich” waters, clays and sea salts contribute magnesium, calcium and friends, but there’s no good evidence that a trace of a nutritional mineral applied to skin does anything nutritional. Your skin gets its minerals from your blood.

If a mineral is there for a specific, named purpose, fine. If it’s there to sound wholesome, that’s all it does.

What “rich in” means on a Canadian label

Legally, not much. Health Canada requires that claims on a cosmetic label be accurate so they don’t mislead people, and it forbids therapeutic claims (treating or preventing a disease, or changing how the body works) on cosmetics; those need a drug or natural health product licence. But there’s no defined threshold for “rich in”, “infused with” or “packed with”. Those are marketing words, and a product can use them with a very small amount of the ingredient.

The ingredient list is more useful than the front of the bottle. Canadian cosmetics must list ingredients by their standard INCI names in descending order by weight, except that anything at 1% or less may be listed in any order at the end. So:

• An ingredient in the first few positions is present in a meaningful amount. Water, glycerin and oils usually lead.
• An ingredient sitting after the preservatives and fragrance is almost certainly at 1% or less. For niacinamide that might still be enough; for a “collagen boost” it means very little either way.
• A vitamin listed as an ester or derivative (ascorbyl palmitate, tocopheryl acetate) is more stable but not necessarily as active as the plain form.

If you want to compare, browse serums and treatments with their full ingredient lists rather than their front labels.

Even the ingredients that do get in produce gradual, moderate change over weeks, not a transformation, and they won’t replace sunscreen or, for a skin condition, treatment. If you’re using skin care to manage a persistent rash, a patch of pigmentation that’s changing, or a spot that won’t heal, see your doctor or pharmacist rather than a new serum.

Small molecules like vitamin C, niacinamide and vitamin E can cross the skin barrier and have measurable, modest effects. Proteins mostly sit on the surface and feel nice; nutritional minerals do nothing from the outside. “Rich in” is a mood, not a measurement, so flip the bottle around and read the list.