Zinc oxide in sunscreen: how it works, nano and safety

What zinc oxide is and what it does in sunscreen

Zinc oxide is a mineral UV filter. A 2011 safety study notes that sunscreens containing zinc oxide or titanium dioxide nanoparticles are effective barriers against UVB damage.¹

It comes in two forms on a label. Plain Zinc Oxide is the ordinary form. Zinc Oxide [nano] is made of nanoparticles, which are extremely small. Snifff has an entry for each.

Does zinc oxide get into your skin?

In a laboratory test on human skin, less than 0.03% of the zinc applied in a nano zinc oxide sunscreen formulation crossed the outer skin layer, not significantly more than with a placebo formulation. No particles could be found in the lower stratum corneum or the living epidermis.²

A study on pigs with UVB sunburn found that zinc oxide nanoparticles stayed in the top one or two layers of the stratum corneum, and no transdermal absorption was detected.¹

There is a caveat. In a 2020 study on human skin removed from the body, zinc oxide nanoparticles were applied to skin with an impaired barrier. After 24 hours, zinc in the living epidermis was 60 to 65 times higher than in the control, and more than 100 times higher after 48 hours. The authors found that the extra zinc was not nano zinc oxide itself, but zinc that had dissolved and then permeated the skin.³

So the lab evidence supports little absorption through intact skin, and more absorption through damaged skin, in a different form. These are laboratory studies on isolated skin and animals, not studies of what happens in everyday use.

What the EU safety committee said about nano zinc oxide

In a 2014 revision of its opinion, the EU’s Scientific Committee on Consumer Safety concluded that zinc oxide nanoparticles with the characteristics described in the dossier, at a concentration of up to 25% as a UV filter in sunscreens, can be considered not to pose a risk of adverse effects in humans after dermal application.⁴

It then added the limit that matters: this does not apply to other uses that might lead to inhalation of the nanoparticles, such as sprayable products. The conclusion also applies only to particles with the stated characteristics, a specified purity, particle size, coating and solubility.⁴

That is the background to Snifff’s summaries above. In plain terms: a cream is one question and a spray is another, because a spray can be breathed in. In the Cosmetics Regulation, Annex VI, entry 30a allows nano zinc oxide at up to 25%, not for applications that may expose the lungs to inhalation.⁵ The India half is Snifff’s. Under the Cosmetics Regulation, an ingredient present as a nanomaterial must be followed by the word ‘nano’ in brackets in the ingredients list.⁵

Zinc oxide in pregnancy and breastfeeding

No pregnancy-specific evidence is not the same as safe, or as unsafe.

Evidence on cosmetic products in pregnancy is limited overall, so ask your doctor or midwife about the specific product you use.⁶

What you will see on the label

Look for Zinc Oxide, and for Zinc Oxide [nano], where the bracketed word marks the nano form. Snifff shows both as Low risk. For the rest of the formula, see what the score means and how to read the list.

If you want to avoid nano ingredients, the bracketed word is where to look, and our guide to reading an ingredient list shows where.

As Snifff shows it

Zinc oxide

Zinc Oxide

Low risk

Pregnancy and nursing

We found no pregnancy- or lactation-specific evidence for this ingredient.

Regulatory gap

The EU bars nano zinc oxide in sprays when it could be inhaled. India does not make the same nano distinction; non-nano cream sunscreens have no gap.

Zinc Oxide [nano]

Low risk

Pregnancy and nursing

We found no pregnancy- or lactation-specific evidence for this ingredient.

Regulatory gap

Both regions permit this nano UV filter at up to 25%. The EU bars sprayable uses that could be inhaled; India does not make the same distinction.

Wording as it appears in the extension, which can change between releases.