A new scientific investigation has cast fresh light on the booming market for so-called 'mineral-only' sunscreens, revealing that many products rely on a hidden palette of chemical ingredients to boost their performance and feel.
The Science Behind Sun Protection
Researchers from UNSW Sydney, including Associate Professor Anna Wang and Professors Jon Beves and Timothy Schmidt, conducted laboratory tests on ten popular mineral sunscreens. Their goal was to demystify how these products achieve high Sun Protection Factor (SPF) ratings and to clarify widespread public confusion about how sunscreens protect skin.
The study, published on Monday 1 December 2025, confirms a crucial point often misunderstood by consumers: both mineral and chemical sunscreens work primarily by absorbing ultraviolet (UV) light, not by reflecting it. The active ingredients in sunscreens fall into two main categories. Inorganic 'mineral' filters, like zinc oxide and titanium dioxide, absorb UV radiation. Organic 'chemical' filters, such as avobenzone and octinoxate, do the same.
Hidden Chemistry in 'Pure' Products
The team's measurements on pure zinc oxide showed strong, even absorption across the UV spectrum. However, when they analysed commercial products, they found telltale signs of additional chemistry. Two out of the ten tested sunscreens marketed as 'mineral only' displayed absorbance 'humps' characteristic of organic chemical filters.
These were identified as butyloctyl salicylate and ethylhexyl methoxycrylene—chemicals added to improve product stability and texture, which also happen to absorb UV light powerfully. Because their primary labelled function is as stabilisers, they do not have to be declared as 'active ingredients' on the bottle.
Expanding their review, the scientists examined 143 sunscreens listed on Australia's Therapeutic Goods Administration register that declared only zinc oxide or titanium dioxide as active ingredients. They discovered that at least 48 of these products (roughly 34%) contained additional chemicals known to strongly absorb UV light.
Why Chemistry is Essential for Effective Sunscreen
The research underscores the formulation challenges sunscreen makers face. Creating a high-SPF product using only mineral filters would require the minerals to constitute around 20% of the sunscreen by weight. This leads to a dense, thick formula that can separate, leave a stark white cast on the skin, and be unpleasant to apply.
To create a lightweight, transparent, and stable lotion that forms an even protective film, chemists incorporate various ingredients. The study compared two 'zinc-only' children's sunscreens: one thick and another with a silky feel. Lab analysis confirmed the silky product contained UV-absorbing molecules that aided spreadability and reduced the white residue.
The SPF of a sunscreen increases after it dries, as a successful formulation creates a uniform film on the skin. Without the right supporting chemistry, the film can bead up, resulting in patchy and unreliable protection.
The authors conclude that the quest for 'clean' or 'natural' products should not equate to avoiding 'chemicals'. Effective, gentle, and cosmetically elegant sunscreens are the result of sophisticated chemistry. A well-formulated product that feels pleasant, spreads evenly, and remains stable is ultimately safer and more reliable than a 'natural' alternative that fails to form a consistent protective barrier.
