A group of researchers at the University of Copenhagen have investigated the mystery and they have come closer to a solution.
- When the sun hits the wet towel, chemical reactions occur. The molecules that hide in the cotton fabric are transformed into scents, says chemist and doctoral student Malte Frydenlund, to DR.
They took an ordinary towel, soaked it in water and then let it dry in the sun on one of the university's balconies. When it was dry, they took the help of an advanced machine to be able to study the scents more closely.
"When the laundry is exposed to ultraviolet light, certain molecules form compounds and processes that often lead to aldehydes and ketones, ie fragrances," Silvia Pugliese, who led the research project, told the New York Times.
Similar processes probably occur on outdoor surfaces, such as bare ground and grass - perhaps part of the reason why it smells good when the sun is on after a rain shower.