It’s important that we feel completely comfortable with the products we choose to buy - especially when they’re applied daily to our own skin or our children’s skin. That concern has always mattered deeply to me. The skin is our largest organ, and while it is an effective barrier, I believe it’s still wise to be mindful of what we put on it. This principle is one of the main reasons I developed Shade All-Natural Sunscreen over ten years ago.
Recently, a study published in 2021 has been widely shared and has understandably caused some alarm. The paper is titled “Zinc oxide-induced changes to sunscreen ingredient efficacy and toxicity under UV irradiation” and can be read in full here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8550398/. I’ve been meaning to address this research properly for some time, and a customer refund request this morning - accompanied by the comment, “I have just been made aware that zinc oxide becomes toxic after exposure to the sun” - made it clear that now is the right time to do so.
When scientific studies circulate online, they’re often summarised or reported without enough context. Headlines can be misleading, and nuance is easily lost. So I’d like to walk through what this study actually investigated, what it found, and how - or whether - it relates to Shade.
To understand the paper, it’s important to look at the study itself rather than second-hand interpretations. The researchers were not testing mineral-only sunscreens, and they were not testing Shade. What they examined was what happens when chemical (organic) UV filters are mixed together and then combined with zinc oxide particles, before being exposed to ultraviolet light in a laboratory setting.
The researchers prepared mixtures of several chemical sunscreen filters — including avobenzone, octisalate, homosalate, octocrylene, oxybenzone, DHHB and bisoctrizole — formulated to achieve an SPF of 15. These mixtures were then combined separately with either nano-sized zinc oxide or non-nano zinc oxide and exposed to UV radiation. The experiments were conducted in solution and did not include the full range of ingredients found in real sunscreens, such as emollients, waxes, surfactants or preservatives.
What they observed was that, under these conditions, some chemical UV filters broke down more quickly when zinc oxide was present. As a result, the mixtures showed reduced UVA protection and, when tested on zebrafish embryos living directly in the solution, increased toxicity. A crucial point - one that’s often missed - is that the toxicity was associated with the breakdown products of the chemical filters, not with zinc oxide itself.
The study did not demonstrate that zinc oxide becomes toxic on skin. It did not test finished sunscreen products as they are used in real life. It did not assess human skin, skin penetration, or topical use in people. Zebrafish embryo testing is a common screening tool in laboratory research, but it does not directly reflect how a sunscreen behaves on intact human skin, particularly one designed to sit on the surface.
This distinction is especially important when it comes to Shade. Shade is a mineral-only sunscreen. We do not use chemical UV filters at all. The interaction examined in this study - zinc oxide accelerating the degradation of chemical filters - simply cannot occur in our formulation because those ingredients aren’t present.
We also use non-nano zinc oxide. Particle size matters. Non-nano zinc oxide has significantly lower surface reactivity than nano-sized forms and has a long history of safe use in products such as nappy rash creams and medical skin barriers. It works by sitting on the surface of the skin and reflecting and scattering UV radiation, rather than being absorbed into the skin or undergoing chemical reactions.
It’s also worth remembering that laboratory experiments are designed to stress-test chemistry under controlled conditions. Real sunscreens are complex formulations, and real skin is a remarkably effective barrier. Zinc oxide in a finished mineral sunscreen is dispersed in oils and waxes and applied to the outermost layer of dead skin cells - not suspended in water and irradiated in isolation.
Zinc oxide remains one of only two sunscreen filters recognised by the U.S. Food and Drug Administration as “Generally Recognised as Safe and Effective” for topical use. This classification is based on decades of human safety data. A broader review of inorganic UV filters, including zinc oxide and titanium dioxide, continues to support their safety and effectiveness when used appropriately.
From a wider, more natural perspective, it’s also worth acknowledging that modern skincare habits are relatively new in the context of human history. Sunscreens, daily washing, and frequent exfoliation are behaviours we’ve adopted recently, and we’re still learning about their long-term effects. I don’t believe any modern practice is beyond future scrutiny. That’s precisely why I remain open, curious, and willing to change if better evidence emerges.
I’m not ideologically attached to zinc oxide. If a sunscreen active were shown to be significantly safer and more effective, I would absolutely consider reformulating. To date, I haven’t found one that meets those criteria. If you’re aware of an alternative you believe is superior, I’m genuinely open to hearing about it.
I hope this helps clarify what this study does - and does not - tell us. I truly appreciate the questions and the care people take when choosing products for themselves and their families. Transparency matters to me, and I stand fully behind Shade and the choices we’ve made in formulating it.
Tania Wedin
Founder & Managing Director
Not the Norm Ltd & Shade All-Natural Sunscreen