EPFL study links personal care products, VOCs and ozone to indoor secondary organic aerosols

Modern personal care products are made with a wide mix of ingredients designed to cover body odour, curb perspiration, moisturise skin, keep hair in place, and add fresh, pleasing fragrances.

In practice, these functions rely on literally hundreds of compounds. From a health standpoint, some ingredients are worrying in their own right. Yet even chemicals generally considered less concerning may still interact with substances around us and create new pollutants whose toxicity is largely unknown.

Researchers led by École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland have now mapped out what gets released when a small selection of widely used personal care products are applied, and how those emissions can transform through reactions in a typical indoor setting.

VOC emissions from everyday personal care products

Across the products tested, the team detected more than 200 different types of volatile organic compound (VOC), with concentrations reaching several parts per million.

While most of these compounds are likely to be benign, particularly at low levels, some notable chemical classes reacted quickly and generated secondary organic aerosols-an outcome that is harder to dismiss as harmless.

"Some molecules 'nucleate' – in other words, they form new particles that can coagulate into larger ultrafine particles that can effectively deposit into our lungs," says EPFL engineer Dusan Licina.

"In my opinion, we still don't fully understand the health effects of these pollutants, but they may be more harmful than we think, especially because they are applied close to our breathing zone. This is an area where new toxicological studies are needed."

Why indoor ozone (O₃) matters

Many modern homes and workplaces contain at least one or two sources of ozone (O₃). Printers and photocopiers commonly emit it, and so-ironically-can air purifiers. Even where there is no ozone-producing equipment, various outdoor pollutants can react in sunlight to form ozone, which may then enter buildings through windows and ventilation.

Although it looks superficially similar to the oxygen we depend on for respiration, ozone’s third oxygen atom makes it comparatively unstable. That instability allows it to react readily with volatile organic compounds such as monoterpenes.

EPFL experiments: adding ozone to product emissions

To explore how much pollution could be produced when ozone reacts with VOCs from personal care products, Licina and colleagues bought and tested a deodorant body spray, hand lotion, roll-on deodorant, perfume, and dry shampoo hair spray, running two separate experimental set-ups.

In the first set of tests, the researchers measured emissions when each product was applied either to an individual standing in a simulated indoor environment, or to a tissue left in the room for an hour. In the second set, they introduced ozone at roughly 35 to 40 parts per billion and tracked what happened when it reacted with emissions from each personal care product.

In every case except one-the roll-on deodorant-the result was a literal particulate “smog”. More worryingly, the particle growth rate was far higher than studies typically report for outdoor air quality, whether in urban settings or remote environments.

With increasing concern about how fine particles in the air can affect health over surprisingly short timescales, it is unsettling to realise we might be generating comparable pollution whenever we do our hair or apply a pleasant perfume.

"I know this is difficult to hear, but we're going to have to reduce our reliance on these products or, if possible, replace them with more natural alternatives that contain fragrant compounds with low chemical reactivity," says Licina.

This research was published in Environmental Science & Technology Letters.