Zinc Oxide in Skincare: What It Does and What It Doesn't

Zinc oxide does three separate jobs, and the labels blur them constantly. It is one of two mineral UV filters permitted in American sunscreen. It is a listed active ingredient in the FDA's skin protectant monograph, with a much narrower permitted claim than the word "protectant" suggests. And it is an odor ingredient in natural deodorants, including ours. Those three jobs do not transfer to each other.

Zinc oxide is an inorganic mineral compound, insoluble in water and largely insoluble in biological fluids. Most of its behavior on skin follows from that one property. It sits on the surface rather than dissolving into it.

Particle size decides how it looks. Larger particles, above roughly 100 nanometers, leave the opaque white cast people associate with lifeguard noses. Manufacturers grind it finer, below about 100 nanometers, specifically to reduce that whiteness. That is the entire reason nano-scale zinc oxide exists in cosmetics, and it is worth holding onto before the nano debate starts.

In the United States, sunscreen is an over-the-counter drug rather than a cosmetic, so its actives are set by federal monograph rather than by marketing. Zinc oxide is on that list. The 1999 monograph text at 21 CFR 352.10(r) permits it up to 25 percent. That part of the code has sat stayed since 2004, but 25 percent is still what the agency calls zinc oxide's maximum eligible concentration.

The FDA's 2019 review proposed zinc oxide as a Category I active, meaning generally recognized as safe and effective, at up to 25 percent. Titanium dioxide got the same proposal. Twelve chemical filters were placed in the category that needs more safety data first. That proposal has not been finalized, so it describes where the agency's thinking sits, not a closed question. What governs sunscreens in the meantime is OTC Monograph M020, the deemed final order the CARES Act created in 2020, which carries the old monograph conditions forward until the FDA replaces them.

Two limits matter for readers. First, SPF belongs to a finished, tested formula, never to an ingredient. Zinc oxide has no SPF of its own, which is why you cannot make a tallow sunscreen at home and honestly print a number on the jar. Second, we do not sell one. A legal sunscreen needs standardized SPF testing and an FDA-licensed manufacturer, which is why FATCO does not make sunscreen.

This is the part that gets stretched. Zinc oxide appears in a second monograph, 21 CFR 347, which covers over-the-counter skin protectants, at 1 to 25 percent under section 347.10(u).

"Skin protectant" sounds broad. The regulation is not. Part 347 defines the category as a product that temporarily protects injured or exposed skin from harmful or annoying stimuli and may help provide relief. For zinc oxide specifically, the permitted "Uses" statement under 347.50(b)(3) is a single indication: drying the oozing and weeping of poison ivy, oak and sumac. Petrolatum and lanolin get the "temporarily protects minor cuts, scrapes, burns" wording. Zinc oxide does not.

The same monograph sets the warnings, which are also the honest routing advice. Keep it out of the eyes and use it externally only. Stop and ask a doctor if the condition worsens, if symptoms last more than seven days, or if they clear up and come back within a few days. That seven-day line is a federal one, not our estimate.

Zinc oxide's familiar role in diaper creams is real and its safety record there is long. The agency cites that large body of topical use as corroborating evidence for its sunscreen safety conclusion. It sits outside Part 347's final rule, though, so it is a separate conversation rather than an extension of this one.

A deodorant containing zinc oxide offers no sun protection whatsoever. It carries no SPF, no Drug Facts panel and no testing. The overlap is the ingredient name only, and the internet blurs this constantly.

What the ingredient does in an underarm is better evidenced than most natural-deodorant claims. A randomized, double-blind, placebo-controlled trial published in Acta Dermato-Venereologica in 2020 tested it on 30 healthy volunteers. Each used a 1.1 percent zinc oxide emulsion on one armpit and a placebo on the other for 13 days. Zinc oxide cut odor-producing Corynebacterium and Staphylococcus hominis counts, and participants rated the treated side less malodorous.

Here is the part usually left out. Skin-surface pH went up significantly on the zinc side, not down and not sideways. The researchers traced that to the hydroxide ions released alongside zinc ions when zinc oxide meets water. They noted the pH shift may work against the antibacterial effect rather than with it. So the common claim that zinc oxide handles bacteria without disturbing skin pH is backwards. It disturbs pH and reduces bacteria anyway.

That is a different route from baking soda in a natural deodorant, which also pushes the underarm alkaline. It is one reason how a natural deodorant affects the underarm microbiome is worth understanding before you switch. Zinc oxide is not a sweat ingredient either. Nothing in the antiperspirant monograph is a zinc compound.

FATCO's Stank Stop deodorant uses it in both formats, and the two labels differ. The cream panel reads non-nano zinc oxide, alongside baking soda in a grass-fed tallow and coconut oil base. The stick panel lists plain zinc oxide with sodium bicarbonate and magnesium hydroxide, so the stick runs three odor actives rather than two.

This is where the ingredient collects the most misinformation, in both directions.

Start with a fact that reframes the argument: the FDA has not established regulatory definitions of nanotechnology, nanomaterial or nanoscale. "Non-nano" on a label is therefore a marketing description, not a regulated claim, and no U.S. agency verifies it.

On absorption, the agency's position is specific. Its review of the dermal penetration studies concluded that zinc oxide does not penetrate human skin to any great extent. Penetration is primarily limited to the upper layers of the non-living stratum corneum, and most of it occurs in folds, furrows and hair follicles. That finding is stated as holding regardless of particle size, including particles in the roughly 1 to 100 nanometer range. Stable-isotope tracing studies did detect a minimal amount of absorbed zinc, at levels orders of magnitude below normal dietary intake. On that basis the FDA is not proposing monograph conditions that treat nanomaterial forms differently.

Do not read that as a clean bill of health either. The same review notes that dermal carcinogenicity studies have not been conducted for zinc oxide, and that published genotoxicity findings are mixed. Its reasoning is that with so little reaching living skin, there is no plausible route for an effect, which is a well-argued inference rather than a direct test.

Particle size does matter in one place, and it is not the skin. For sprays, the agency proposes that any sunscreen dispensing particles smaller than 5 micrometers would not qualify. The real inhalation risk is the size of what leaves the can. The sensible non-nano caution is about breathing loose powder, not about absorbing a cream.

It suits people who want mineral-only UV filters and people whose skin reacts to chemical ones. In the FDA's review, test material containing up to 25 percent zinc oxide produced no irritant, photoirritant, allergic or photoallergic reactions in human dermal safety studies. That is a stronger tolerance record than most actives carry. If chemical sunscreens sting, zinc oxide belongs in a calmer routine for reactive skin.

It does not suit anyone who wants an invisible finish, particularly on deeper skin tones. The white cast is not a formulation flaw, it is what the mineral looks like, and higher percentages look whiter. It does not suit anyone who wants to sweat less, since it does nothing to the sweat duct. And it does not suit anyone treating a real skin condition on their own, because the monograph indication is one narrow use with a seven-day stop-and-ask-a-doctor line attached.

We use zinc oxide for exactly one job and we would rather say which. In Stank Stop it works on the bacteria behind underarm odor, on a base of grass-fed tallow, coconut oil and shea butter that keeps the skin conditioned instead of chalky. It is not sun protection, it is not a sweat blocker and it is not a treatment. The cream and the stick carry slightly different odor actives, and both print the full panel where you can read it before you buy.