When hairstylists use flat irons to smooth and style hair, they heat the hair to about 200 degrees Celsius. At that temperature, the liquid products they apply release tiny particles into the air called aerosols. Those aerosols can end up in the stylist's lungs. For years, there was no good way to study exactly how harmful those particles might be without testing on animals. Now researchers in Hannover, Germany have found a better way.

Scientists at the Fraunhofer Institute for Toxicology and Experimental Medicine ITEM have developed a testing method that uses actual human lung cells instead of animals. The team created a system called the P.R.I.T. ExpoCube, which lets them expose human cells to aerosols in a controlled setting. The cells are grown at the boundary between air and liquid, exactly how they would sit inside a person's respiratory tract.

To test hair products, researchers apply the liquid to strands of real human hair and smooth it with a heated flat iron. The aerosols released are then channeled into the ExpoCube, where the human lung cells wait on the other side.

Detlef Ritter, a research scientist at Fraunhofer ITEM, explained that the same method could be used to test all kinds of inhaled substances. In an earlier project, his team was able to reformulate a room spray by finding and replacing a single problematic ingredient. "We managed to identify and replace an unsuitable component in the spray product," Ritter said.

The team tested four different hair product formulations under the industrial contract. Some showed a higher potential to irritate the lungs than others. Previously, it was impossible to establish a clear connection between a specific product, how it was applied, and what health effects hairstylists might experience. Now, companies can test products before they hit the market and improve them if needed.

The timing matters. The EU now allows only testing methods that do not involve animals for checking the safety of cosmetics. This new in vitro method, meaning testing done outside a living organism, fits that requirement perfectly. It also follows what's called a "safe-by-design" approach, which means safety is built into products from the very beginning of development, not added on at the end.

For the beauty industry, this means fewer animals in laboratories and hairstylists who can breathe a little easier knowing the products they use every day have been checked thoroughly using human cells.