What's inside
What's inside
Key Ingredients
Benefits
Concerns
Ingredients Side-by-side
Water
Skin ConditioningZinc Oxide
Cosmetic ColorantPropanediol
SolventButyloctyl Salicylate
Skin ConditioningCyclohexasiloxane
EmollientCaprylyl Methicone
Skin ConditioningCoco-Caprylate/Caprate
EmollientPropylheptyl Caprylate
EmollientPolyglyceryl-3 Polydimethylsiloxyethyl Dimethicone
Skin ConditioningMethyl Trimethicone
Skin ConditioningMethyl Methacrylate Crosspolymer
Isododecane
Emollient1,2-Hexanediol
Skin ConditioningPolymethylsilsesquioxane
Acetyl Tetrapeptide-2
Skin ConditioningCopper Tripeptide-1
Skin ConditioningAcetyl Hexapeptide-8
HumectantHyaluronic Acid
HumectantSodium Hyaluronate
HumectantHydrolyzed Hyaluronic Acid
HumectantHelianthus Annuus Seed Oil
EmollientFerulic Acid
AntimicrobialSolanum Lycopersicum Fruit Extract
AntioxidantRosmarinus Officinalis Leaf Extract
AntimicrobialDipotassium Glycyrrhizate
HumectantPanthenol
Skin ConditioningAllantoin
Skin ConditioningGlycerin
HumectantTocopherol
AntioxidantEthyl Ferulate
AntioxidantDisteardimonium Hectorite
StabilisingMagnesium Sulfate
Lauryl Polyglyceryl-3 Polydimethylsiloxyethyl Dimethicone
Skin ConditioningTriethylhexanoin
MaskingPolyglyceryl-2 Dipolyhydroxystearate
Skin ConditioningTriethoxycaprylylsilane
Glyceryl Caprylate
EmollientDimethicone
EmollientLauryl Dimethicone/Polyglycerin-3 Crosspolymer
CleansingCaprylyl Glycol
EmollientHydroxyacetophenone
AntioxidantButylene Glycol
HumectantDipropylene Glycol
HumectantSilica
AbrasiveEthyl Hexanediol
SolventEthylhexylglycerin
Skin ConditioningSodium Citrate
BufferingPhenoxyethanol
PreservativeWater, Zinc Oxide, Propanediol, Butyloctyl Salicylate, Cyclohexasiloxane, Caprylyl Methicone, Coco-Caprylate/Caprate, Propylheptyl Caprylate, Polyglyceryl-3 Polydimethylsiloxyethyl Dimethicone, Methyl Trimethicone, Methyl Methacrylate Crosspolymer, Isododecane, 1,2-Hexanediol, Polymethylsilsesquioxane, Acetyl Tetrapeptide-2, Copper Tripeptide-1, Acetyl Hexapeptide-8, Hyaluronic Acid, Sodium Hyaluronate, Hydrolyzed Hyaluronic Acid, Helianthus Annuus Seed Oil, Ferulic Acid, Solanum Lycopersicum Fruit Extract, Rosmarinus Officinalis Leaf Extract, Dipotassium Glycyrrhizate, Panthenol, Allantoin, Glycerin, Tocopherol, Ethyl Ferulate, Disteardimonium Hectorite, Magnesium Sulfate, Lauryl Polyglyceryl-3 Polydimethylsiloxyethyl Dimethicone, Triethylhexanoin, Polyglyceryl-2 Dipolyhydroxystearate, Triethoxycaprylylsilane, Glyceryl Caprylate, Dimethicone, Lauryl Dimethicone/Polyglycerin-3 Crosspolymer, Caprylyl Glycol, Hydroxyacetophenone, Butylene Glycol, Dipropylene Glycol, Silica, Ethyl Hexanediol, Ethylhexylglycerin, Sodium Citrate, Phenoxyethanol
Water
Skin ConditioningCyclohexasiloxane
EmollientEthylhexyl Methoxycinnamate
UV AbsorberSilica
AbrasiveEthylhexyl Salicylate
UV AbsorberGlycerin
HumectantTitanium Dioxide
Cosmetic ColorantPEG-10 Dimethicone
Skin ConditioningCaprylyl Methicone
Skin ConditioningZinc Oxide
Cosmetic ColorantPolymethyl Methacrylate
Pentylene Glycol
Skin ConditioningGlyceryl Glucoside
HumectantPachyrhizus Erosus Root Extract
Skin Conditioning1,2-Hexanediol
Skin ConditioningCetyl PEG/PPG-10/1 Dimethicone
EmulsifyingMagnesium Sulfate
CI 77007
Cosmetic ColorantAllantoin
Skin ConditioningTrimethylsiloxysilicate
EmollientAluminum Hydroxide
EmollientStearic Acid
CleansingHydroxyacetophenone
AntioxidantOctyldodecanol
EmollientDisteardimonium Hectorite
StabilisingButylene Glycol
HumectantGlyceryl Caprylate
EmollientDipotassium Glycyrrhizate
HumectantDimethicone
EmollientHelianthus Annuus Seed Oil
EmollientPropanediol
SolventSodium Phytate
Triethoxycaprylylsilane
Methyl Diisopropyl Propionamide
MaskingPolyhydroxystearic Acid
EmulsifyingBHT
AntioxidantNeopentyl Glycol Diethylhexanoate
EmollientTremella Fuciformis Extract
HumectantLavandula Angustifolia Flower/Leaf/Stem Extract
MaskingEthyl Ferulate
AntioxidantAscorbyl Glucoside
AntioxidantRosmarinus Officinalis Leaf Extract
AntimicrobialTocopherol
AntioxidantEthylhexylglycerin
Skin ConditioningMagnesium Chloride
Panthenol
Skin ConditioningCalcium Gluconate
HumectantPyridoxine Hcl
Skin ConditioningYeast Extract
Skin ConditioningCyanocobalamin
Skin Conditioning3-O-Ethyl Ascorbic Acid
Skin ConditioningTerminalia Ferdinandiana Fruit Extract
AntioxidantWater, Cyclohexasiloxane, Ethylhexyl Methoxycinnamate, Silica, Ethylhexyl Salicylate, Glycerin, Titanium Dioxide, PEG-10 Dimethicone, Caprylyl Methicone, Zinc Oxide, Polymethyl Methacrylate, Pentylene Glycol, Glyceryl Glucoside, Pachyrhizus Erosus Root Extract, 1,2-Hexanediol, Cetyl PEG/PPG-10/1 Dimethicone, Magnesium Sulfate, CI 77007, Allantoin, Trimethylsiloxysilicate, Aluminum Hydroxide, Stearic Acid, Hydroxyacetophenone, Octyldodecanol, Disteardimonium Hectorite, Butylene Glycol, Glyceryl Caprylate, Dipotassium Glycyrrhizate, Dimethicone, Helianthus Annuus Seed Oil, Propanediol, Sodium Phytate, Triethoxycaprylylsilane, Methyl Diisopropyl Propionamide, Polyhydroxystearic Acid, BHT, Neopentyl Glycol Diethylhexanoate, Tremella Fuciformis Extract, Lavandula Angustifolia Flower/Leaf/Stem Extract, Ethyl Ferulate, Ascorbyl Glucoside, Rosmarinus Officinalis Leaf Extract, Tocopherol, Ethylhexylglycerin, Magnesium Chloride, Panthenol, Calcium Gluconate, Pyridoxine Hcl, Yeast Extract, Cyanocobalamin, 3-O-Ethyl Ascorbic Acid, Terminalia Ferdinandiana Fruit Extract
Ingredients Explained
These ingredients are found in both products.
Ingredients higher up in an ingredient list are typically present in a larger amount.
1,2-Hexanediol is a synthetic liquid and another multi-functional powerhouse.
It is a:
- Humectant, drawing moisture into the skin
- Emollient, helping to soften skin
- Solvent, dispersing and stabilizing formulas
- Preservative booster, enhancing the antimicrobial activity of other preservatives
Allantoin is a soothing ingredient known for its protective and moisturizing properties; it's basically a quiet workhorse ingredient you can find in a huge range of cosmetics.
Though it can be derived from the comfrey plant, allantoin is produced synthetically for cosmetic products to ensure purity.
Research shows it can encourage your skin cells to turn over and renew by stimulating keratinocyte and fibroblast proliferation.
It also has mild keratolytic properties to help loosen and shed dead skin cells without being harsh.
Studies also suggest allantoin can help calm inflammation by dialing down some of the chemical signals your skin sends out when it is irritated.
This ingredient is typically used in the 0.1-0.5% range, and the FDA recognizes it as a skin protectant in OTC products up to 2%.
Overall, allantoin is a wonderful addition to most routines; it is stable across a wide pH range (~4-8), works well with other ingredients, and is considered non-sensitizing/non-irritating.
Fun fact: Allantoin is naturally occurring in comfrey root, beets, chamomile, and wheat sprouts. Our bodies even produce it as a byproduct of uric acid metabolism.
Learn more about AllantoinButylene Glycol (or BG) is used within cosmetic products for a few different reasons:
Overall, Butylene Glycol is a safe and well-rounded ingredient that works well with other ingredients.
Though this ingredient works well with most skin types, some people with sensitive skin may experience a reaction such as allergic rashes, closed comedones, or itchiness.
Learn more about Butylene GlycolCaprylyl Methicone is a synthetic and lightweight silicone fluid. It gives products a silky, dry-touch finish without the heaviness of pure oils.
Though the EU CosIng Database lists this ingredient as a skin conditioner, it is also used for sensory reasons. It spreads easily, cuts greasiness, and reduces tackiness.
This ingredient is volatile which means it will mostly evaporate (but it evaporates slower than older cyclomethicones, like Cyclotetrasiloxane).
Typical concentration ranges from 1-30% depending on if it's being used to tweak the feel of a product or acting as the main emollient.
Learn more about Caprylyl MethiconeCyclohexasiloxane is a type of silicone more commonly known as D6. It is an emollient and solvent.
Cyclohexasiloxane is used to evenly distribute ingredients throughout the product. When applied to the skin, Cyclohexasiloxane evaporates and leaves behind a silky feel.
As an emollient, it can help the skin feel soft and hydrated. It is also used to reduce frizz in hair products.
Learn more about CyclohexasiloxaneDimethicone is a type of synthetic silicone created from natural materials such as quartz. It is also known as polydimethylsiloxane.
What it does:
Dimethicone comes in different viscosities:
Depending on the viscosity, dimethicone has different properties.
Ingredients lists don't always show which type is used, so we recommend reaching out to the brand if you have questions about the viscosity.
This ingredient is unlikely to cause irritation because it does not get absorbed into skin. However, people with silicone allergies should be careful about using this ingredient.
Note: Dimethicone may contribute to pilling. This is because it is not oil or water soluble, so pilling may occur when layered with products. When mixed with heavy oils in a formula, the outcome is also quite greasy.
Learn more about DimethiconeDipotassium Glycyrrhizate comes from licorice root.
Extracts of licorice have demonstrated to have antibacterial, anti‐inflammatory, antiviral, antioxidant properties.
One component, glabridin, has extra potent antioxidant and soothing properties. It has also been found to block pigmentation from UVB rays in guinea pigs.
Licorice Root also contains a flavonoid. Flavonoids are a natural substance from in plants. Flavonoids also have antioxidant properties.
Another component, glycyrrhizin, has been found to have anti-inflammatory and antimicrobial benefits. This may make licorice root extract effective at treating acne. However, more research is needed to support this.
Liquiritin is one of the flavone compounds found in licorice. It has been found to help lighten skin by preventing tyrosinase from reacting with tyrosine. When the two react, protein is converted to melanin. Melanin is the substance in your body that gives your features pigmentation.
Licorice root is native to Southern Europe and Asia. It has been used in traditional Chinese medicine to help with respiratory issues.
Learn more about Dipotassium GlycyrrhizateDisteardimonium Hectorite comes from the clay mineral named hectorite. It is used to add thickness to a product.
It can also help stabilize a product by helping to disperse other ingredients.
Hectorite is a rare, white clay mineral.
Learn more about Disteardimonium HectoriteEthyl ferulate is an antioxidant derived from ferulic acid and ethyl alcohol. You'll most likely see this ingredient in sunscreens.
One study from 2014 found a concentration of 10% showed a similar SPF to Benzimidazole. Though this is considered a chemical UV filter, this ingredient is not listed as so. This is due to regulatory loopholes. You'll likely find this ingredient in "100% mineral" sunscreens.
This ingredient is typically found in concentrations between 0.5-1%. It is usually created synthetically or from rice bran oil.
Learn more about Ethyl FerulateEthylhexylglycerin is created from glycerin. It is a multitasker ingredient that:
The CIR Expert Panel found minimal skin absorption or sensitization of any kind in a safety assessment. Though this ingredient is considered well-tolerated, a small number of cases of allergic dermatitis have been published since 2002. Just be sure to patch test if you are unsure.
Industry-reported use ranges from 8% in rinse-off products and 2% in leave-on formulations.
Learn more about EthylhexylglycerinGlycerin (or glycerol) is a compound naturally found in your skin. It's a powerhouse humectant that pulls water into the stratum corneum.
Topically, glycerin does several things at once:
Your skin makes glycerin on its own (mostly from sebaceous oil breakdown) and shuttles it to your outermost layer of skin, or your epidermis, via aquaporin-3.
Aquaporin-3 is a transporter that is essential for normal skin hydration, elasticity, and repair. Interestingly, mice lacking in AQP3 have dry and less elastic skin that can be fully corrected with glycerin.
This ingredient is non-irritating, plays well with almost every ingredient, and works across all skin types. Typical use is anywhere between 3-10% but can go up to 79% in some leave-on products.
Just know very high concentrations (>40%) can feel tacky in low humidity.
Glycerin is the name for this ingredient in American English. British English uses Glycerol/Glycerine.
Learn more about GlycerinGlyceryl Caprylate comes from glycerin and caprylic acid. It is an emollient, co-emulsifier, and preservative booster.
Its short C8 fatty acid chain makes it behave differently from its longer-chain emollient cousins like Glyceryl Stearate. It feels more lightweight, fast-absorbing, and silky instead of rich and waxy.
As a co-emulsifier, its "head" and "tail" sit at the oil-water interface. But overall, the short C8 tail and not being water soluble means it doesn't really have the muscle to emulsify a formula on its own. That's why you'll often see it paired with a primary emulsifier like Cetearyl Glucoside.
Interestingly, Glyceryl Caprylate acts as a preservative booster. This is because its fatty-acid backbone disrupts microbial lipid membranes. It shows excellent activity against bacteria and yeast but is weaker against mold.
Typical concentrations range from 0.5-1% and this ingredient is generally non-irritating.
Because this ingredient has a C8 fatty acid chain, it is outside the range that the Malassezia yeast metabolizes (making it fungal acne safe).
Learn more about Glyceryl CaprylateHelianthus Annuus Seed Oil is a plant oil derived from the seeds of a sunflower.
It is rich in fatty acids, primarily linoleic acid and oleic acid. This gives it emollient and skin conditioning properties.
The reason this ingredient is so effective is because it forms a thin film on the skin that reduces transepidermal water loss (TEWL) while supplying linoleic acid to the stratum corneum to improve barrier strength.
The high linoleic acid content is particularly noteworthy for acne-prone skin.
Research suggests that acne-prone skin tends to be deficient in linoleic acid in sebum. Topical application may help replenish this to support a healthier follicular environment and less comedone-promoting sebum.
One randomized study found sunflower seed oil preserved skin barrier integrity in adult volunteers with and without atopic dermatitis (outperforming olive oil).
This ingredient is well-studied, gentle, and an effective emollient suitable for most skin types.
On fungal acne: This ingredient may not be Fungal acne (Malassezia folliculitis) safe. This is because it contains fatty acids with carbon chain lengths in the C11-C24 range.
Learn more about Helianthus Annuus Seed OilHydroxyacetophenone is a small phenolic molecule that earns its place in a formulas as an antioxidant and preservative booster.
As a phenol, it is able to neutralize free radicals to protect both the product and the skin from oxidative stress.
Though it can't kill microbes on its own, it works as a good supporting agent when combined with other preservatives like Phenoxyethanol or 1,2-Hexanediol.
This ingredient naturally occurs as piceol in Norwegian spruce needles (~0.4-1.1% dry weight and in cloudberries). Though the cosmetic-grade material is synthesized for purity and consistency.
You'll usually see it used at low levels and suppliers recommend up to 1% added to a water phase.
Safety testing was done at concentrations like 0.05% in SPF products and 0.5% in a Human Repeated Insult Patch Test. The safety evidence is assuring; this ingredient is safe for cosmetics in current use and also holds safety status as a food flavoring as well.
An honest caveat: the "soothing" and "anti-inflammatory" claims come mostly from supplier marketing rather than published clinical trials. The Cosmetic Ingredient Review's own literature search found no useful efficacy studies on this ingredient.
So the antioxidant and preservative-boosting roles are the well supported ones while the calming benefit is plausible but thinly evidenced.
Overall, this is a well-tolerated, low-irritation multitasker that quietly helps a formula stay fresh and stable.
Learn more about HydroxyacetophenoneMagnesium Sulfate is a salt. More specifically, it is an epsom salt, or the bath salt used to help relieve muscle aches.
Despite having ‘sulfate’ in the name, it isn’t a surfactant or cleansing agent like sodium lauryl sulfate. Unlike those sulfates, magnesium sulfate doesn’t have the same cleansing or foaming properties (it's simply a type of salt).
In cosmetics, Magnesium Sulfate is used to thicken a product or help dilute other solids. It is a non-reactive and non-irritating ingredient.
One study shows magnesium deficiency may lead to inflammation of the skin. Applying magnesium topically may help reduce inflammation.
You can find this ingredient in sea water or mineral deposits.
Learn more about Magnesium SulfatePanthenol is a common ingredient that helps hydrate and soothe the skin. It is found naturally in our skin and hair.
There are two forms of panthenol: D and L.
D-panthenol is also known as dexpanthenol. Most cosmetics use dexpanthenol or a mixture of D and L-panthenol.
Panthenol is famous due to its ability to go deeper into the skin's layers. Using this ingredient has numerous pros (and no cons):
Like hyaluronic acid, panthenol is a humectant. Humectants are able to bind and hold large amounts of water to keep skin hydrated.
This ingredient works well for wound healing. It works by increasing tissue in the wound and helps close open wounds.
Once oxidized, panthenol converts to pantothenic acid. Panthothenic acid is found in all living cells.
This ingredient is also referred to as pro-vitamin B5.
Learn more about PanthenolPropanediol is an all-star ingredient. It softens, hydrates, and smooths the skin.
It’s often used to:
Propanediol is not likely to cause sensitivity and considered safe to use. It is derived from corn or petroleum with a clear color and no scent.
Learn more about PropanediolThis is a botanical extract from the rosemary plant (the same one you cook with). In skincare, it mostly works as a skin conditioning agent.
Its activity comes from a handful of polyphenols, carnosic acid, carnosol, and rosmarinic acid. Almost 90% of the antioxidant activity of this ingredient can be attributed to canosol and carnosic acid.
These compounds protect your skin two ways:
1) They fight off free radicals, or the unstable molecules from things like sun and pollution that age and damage skin.
2) They help calm inflammation by switching off the chemical signals that tell skin to get red and irritated.
Lab studies also suggest that rosmarinic acid may help protect collagen and slow sugar-related damage to it.
The Cosmetic Ingredient Review has concluded rosemary-derived ingredients to be safe when formulated to be non-sensitizing.
Rosemary can occasionally cause allergic contact dermatitis (due to carnosol), so be sure to patch test if you have reactive or fragrance-sensitive skin.
Learn more about Rosmarinus Officinalis Leaf ExtractSilica, also known as silicon dioxide, is a naturally occurring mineral. It is used as a fine, spherical, and porous powder in cosmetics.
Though it has exfoliant properties, the function of silica varies depending on the product.
The unique structure of silica enhances the spreadability and adds smoothness, making it a great texture enhancer.
It is also used as an active carrier, emulsifier, and mattifier due to its ability to absorb excess oil.
In some products, tiny microneedles called spicules are made from silica or hydrolyzed sponge. When you rub them in, they lightly polish away dead skin layers and enhance the penetration of active ingredients.
Learn more about SilicaTocopherol is a fat-soluble antioxidant known as Vitamin E.
You'll find this ingredient in the vast majority of skincare (for good reason). It works to neutralize free radicals, or unstable molecules generated by UV exposure, pollution, and other environmental stressors, before they can cause oxidative damage to your skin cells.
Topically applied tocopherol has been shown to protect against UV damage by ramping up the skin's own natural defense enzymes.
It also acts as a skin conditioning agent; some studies show that regular topical use can improve the skin's water-binding capacity over 2-4 weeks.
This ingredient is especially loved for being a team player. When combined with Vitamin C, the photoprotective effect of both ingredients roughly doubles and the combo also helps reduce UV-induced DNA damage.
This ingredient has some brightening potential but it's more of a prevention ingredient than spot-fader. Cell studies show it can slow down melanin production but it's worth noting that it's not the most powerful brightener out there.
In formulations, it also serves as a stabilizer that helps protect other oxidation-prone ingredients from degrading.
Concentrations usually range from 0.1-1% in most leave-on products.
Learn more about TocopherolTriethoxycaprylylsilane is a silicon-based surface modifier that makes sunscreens feel silky and makeup stay put.
Its main job is to coat mineral particles like titanium dioxide, zinc oxide, and color pigments in a thin, oily layer so they spread smoothly, don't clump, and stick to skin better.
This ingredient is typically used at low levels (up to 2.5% in eyeshadow and 1% in lipstick).
Learn more about TriethoxycaprylylsilaneWater. It's the most common cosmetic ingredient of all. You'll usually see it at the top of ingredient lists, meaning that it makes up the largest part of the product.
So why is it so popular? Water most often acts as a solvent - this means that it helps dissolve other ingredients into the formulation.
You'll also recognize water as that liquid we all need to stay alive. If you see this, drink a glass of water. Remember to stay hydrated!
Learn more about WaterZinc Oxide (ZO) is a mineral broad-spectrum UV filter and the broadest-spectrum filter recognized by the FDA. It covers everything from UVB through to long-wave UVA.
On top of sun protection, it has skin protectant and skin-soothing properties too.
Here's a myth worth busting: mineral filters are usually described as working by "reflecting" or "bouncing" UV off your skin.
That's mostly not true: when researchers actually measured it, ZO and Titanium Dioxide reflect only about 4-5% of UV (less than SPF 2 worth of protection).
The vast majority of the work (~95%) is done by absorption, similar to chemical UV filters. ZO is a semiconductor that absorbs UV photos through its energy band gap.
So the old "physical blocker vs. chemical absorber" framing is really an oversimplification.
Zinc Oxide is one of the most effective broad-spectrum UV filters out there. It protects across UVB, UVA2, and UVA1 with a flat, even absorption curve across the whole UVA-UVB range.
That uniform UVA coverage is its standout feature; titanium dioxide skews more toward UVB as its particle size drops so ZO gives more consistent and extended UVA protection.
It's also very photostable. As an inorganic oxide, ZO doesn't break down in sunlight the way some organic filters can, so it holds up over a day of wear.
This ingredient is gentle and soothing, making it go-to for sunscreens aimed at sensitive skin, rosacea, or ecezma-prone skin, babies, and children.
It's also unlikely to cause the "eye sting" that some sunscreen ingredients are known for, and regulatory agencies broadly consider it non-toxic and safe for topical use.
Beyond sun protection, ZO is also a recognized OTC skin protectant. It forms a breathable barrier that shields skin from moisture and irritation while supporting healing. This is why you'll see it as a classic active in diaper rash creams.
The only downside to ZO is that it can leave a visible white cast, especially on deeper skin tones. This is the main reason mineral sunscreens have historically felt less cosmetically elegant than chemical or hybrid formulas.
Zinc Oxide comes in both non-nano and nano forms. The dividing line is 100nm and anything under is classified as a nanomaterial by the EU.
The nano version scatters less visible light which cuts down white case and gives a lighter, more wearable texture.
Another thing worth understanding about formulation:
Uncoated ZO has some inherent photocatalytic activity. This just means it can generate reactive oxygen species under UV. It's exactly why cosmetic-grade ZO is almost always surface-coated; this coating suppresses that reactivity and improves how the powder disperses and feels.
A well-formulated coated ZO largely sidesteps this issue.
Zinc Oxide is commonly used anywhere from 10% up to the regulatory maximum in sunscreens (25%).
Mineral-only broad-spectrum products often land in the 15-25% range to hit higher SPF and UVA values. Keep in mind SPF performance depends heavily on particle size, dispersion, and the rest of the formula, and not just the percentage.
As an OTC skin protectant like diaper creams, ZO typically runs higher at roughly 10-40%.
This ingredient is generally easy to work with and doesn't photodegrade.
The only thing to know is that uncoated ZO can be a bit reactive in a formula.
Under UV, it can break down sensitive ingredients like other actives or UV filters. This is another reason coated versions are standard. ZO can also react with very acidic ingredients or throw off stability of some creams. A good formula will get around this with the right coatings and dispersion.
The EU's Scientific Committee on Consumer Safety has concluded that ZO nanoparticles "can be considered to not pose any risk of adverse effects in humans after application on healthy, intact or sunburnt skin".
You might hear that ZO is "toxic"; this is because an in-vitro (test tube) study suggested micronized ZO had potential phototoxicity. In vivo (human) investigations have disputed this and the results have come back reassuring.
So does ZO penetrate skin? The short answer is no, not in any way that matters.
The most relevant evidence comes from real-world human studies: in one, volunteers applied ZO nanoparticle sunscreen hourly for six hours and daily for five days. The advanced imaging showed the particles stayed on the surface and never reached the living epidermis, and no cellular toxicity was found.
Other in-vivo and ex-vivo work agree; ZO nanoparticles don't cross the stratum corneum, even on flexed, massaged, or barrier-impaired skin.
A small amount of solubilized zinc ions can dissolve off the particles and enter the upper skin. But the quantities are tiny compared to the zinc already naturally present in your body, and studies haven't found this to cause local toxicity.
The sunscreen bans you've heard of (like Hawaii's) are aimed at two chemical filters, Oxybenzone and Octinoxate. ZO itself it not banned and is often recommended instead.
So far, there's no solid evidence that any form of ZO harms reefs. It is an ongoing and active area of study, and worth keeping an eye on.
If you're traveling somewhere with these rules, a non-nano mineral sunscreen is the safe bet.
Learn more about Zinc Oxide