Scientists have figured out what causes sunscreen to leave bright red marks on fabrics
If you’ve ever done laundry after a day outside, you’ve probably seen it happen: sunscreen and bleach turn your clothes a stubborn red. Now, chemists have uncovered the surprising molecule behind this colour change, and their findings could help improve the future of sunscreen products and environmental safety.
Researchers set out to solve the mystery of why certain sunscreens create red staining when exposed to sodium hypochlorite, the main chemical in bleach. They focused on a popular UVA-filtering element called diethylaminohydroxybenzoyl hexyl benzoate, often referred to as “1” in the lab. This compound is widely used because it provides strong protection against UVA rays and does not break down in sunlight.
As soon as the researchers mixed the pure sunscreen ingredient with bleach, it produced a bright red compound. Previous studies suggested that a dichlorinated compound, known as 2, was respon sible. However, detailed NMR results and computer modelling showed that the real cause of the red colour was another chlorinated molecule, labelled 3, which had been overlooked before.
This red molecule forms through a surprising reaction called ipso-dichlorination, in which chlorine takes over a position on the aromatic ring that is unusual. The researchers figured out the structure of this molecule using advanced spectroscopy techniques and backed this up with quantum-level calculations. Their computed data closely matched the compound’s actual colour, confirming they had identified it correctly.
Strangely, molecule 3, the red colour molecule, is an intermediate. In spite of its rapid formation, it is unstable. Under alkaline conditions, the bright red colour timidly changes into a colourless compound, hence making it more stable. This is a factual explanation of the red stains fading after long soaking and washing.
The professionals made a type of sunscreen ingredient that doesn’t go through that unusual chlorination reaction. As anticipated, on mixing with bleach, this changed product didn’t produce the red colour. Hence, this suggests the redesign of the sunscreen ingredient results that don’t cause the stain.
Stained cloths are not the only problem. Atmospheric concerns are the issue as well. Every day chores are the reason for the sunscreen ingredients to end up in wastewater. Disinfectants like hypochlorite react with these chemicals to form chlorinated molecules with hidden environmental factors. Hence, some potentially toxic and long-lasting chlorinated aromatic compounds need an in-depth study.
Items used in daily work can surprisingly have chemical reactions after being used in household work or wastewater treatments. As sunscreens provide a protective layer against UV, the professionals pinpointed the need to understand how the ingredients act in the environment.
The invention of the fusion between the sunscreen and bleach not only clears up the household misery but also creates a safer, cleaner, and less stain-prone UV filter for the future.
