When researchers in Sweden tested dozens of garments from popular clothing lines, they found thousands of chemicals leftover from the manufacturing process.

Hundreds of the chemicals weren't listed by manufacturers. Scientists say these chemicals may be manufacturing byproducts or residues picked up during transport.

"Exposure to these chemicals increases the risk of allergic dermatitis, but more severe health effect for humans as well as the environment could possibly be related to these chemicals," Giovanna Luongo, an analytical chemist at Stockholm University, said in a press release. "Some of them are suspected or proved carcinogens and some have aquatic toxicity."

Luongo was inspired to explore the subject of clothing toxicity by the more obvious problem of textile wastewater pollution. If chemicals used during the clothing manufacturing process are such a problem for wastewater managers, she wondered, couldn't they be a problem in the finished product?

Researchers are now in the second stage of testing. Luongo and her colleagues identified several categories of chemicals they want study further. Their decision making was based on chemicals' frequency of occurence, quantity, toxicity and potential for skin penetration.

Two main classes of chemicals, quinolines and aromatic amines, were found in polyester, while cotton hosted significant concentrations of benzothiazoles.

Researchers tested clothes before and after washing. Some substances that wash off could be potentially harmful to the aquatic environment.

"We have only scratched the surface, this is something that has to be dealt with. Clothes are worn day and night during our entire life," said Conny Ostman, also an analytical chemist. "We must find out if textile chemicals go into our skin and what it means to our health. It is very difficult to assess and requires considerably more research."

The latest analysis is part of Luongo's thesis work, which she recently published online.