Phthalates and other potentially harmful chemicals are found in many cosmetics that girls and women use regularly.
The study - led by Kim Harley, associate director of the University of California-Berkeley Center for Environmental Research and Children's Health - is published in the journal Environmental Health Perspectives.
According to the Centers for Disease Control and Prevention (CDC), phthalates are a group of chemicals used in plastics, flooring, detergents, soaps, shampoos, hair sprays, cosmetics and nail polishes.
Once they enter the body, they are then converted into metabolites that pass in the urine.
Although the health effects of exposure to these chemicals are largely unknown, some types have been shown to affect the reproductive system in laboratory animals.
The CDC say "more research is needed to assess the human health effects of exposure to phthalates," which is not particularly comforting for consumers.
Furthermore, the CDC have previously found significant levels of phthalate metabolites in the general population, which suggests that phthalate exposure is far-reaching in the US population.
Previous research from the organization has also found that adult women have higher urinary metabolite levels than men, since phthalates are used in personal care products that are used more frequently by women.
Metabolites of chemicals decreased after 3 days
The researchers of this latest study wanted to investigate how switching cosmetic products - to those labeled free of phthalates, parabens, triclosan and oxybenzone - would affect urinary metabolites in adolescent girls.
These chemicals have been shown in previous animal studies to intervene in the body's endocrine system.
"Because women are the primary consumers of many personal care products," says Harley, "they may be disproportionately exposed to these chemicals." She adds:
"Teen girls may be at particular risk since it's a time of rapid reproductive development, and research has suggested that they use more personal care products per day than the average adult woman."
To conduct their investigation, the researchers analyzed urine samples of 100 Latina teenagers who were participating in the Health and Environmental Research on Makeup of Salinas Adolescents (HERMOSA) study.
They measured metabolites in urine samples both before and after a 3-day trial, in which the girls used the products with fewer chemicals.
Results showed that metabolites of diethyl phthalate - used in fragrances - decreased by 27%, while methyl and propyl parabens - used as preservatives in cosmetics - decreased by 44% and 45%, respectively. Meanwhile, triclosan - found in soaps and toothpaste - and benzophenone-3 (BP-3) - found in sunscreens - both decreased by 36%.
"The results of the study are particularly interesting on a scientific level," says study co-director Kimberly Parra, "but the fact that high school students led the study set a new path to engaging youth to learn about science and how it can be used to improve the health of their communities."
She adds that after learning about the study outcomes, many of the girls wanted to educate the community and presented their cause to legislatures in Sacramento, CA.
Consumer techniques can reduce personal exposure
Interestingly, another result of the study revealed a minor increase in concentrations of two less common parabens - ethyl and butyl parabens - but the researchers say the levels were small and could be down to either accidental contamination or a substitution not indicated on the product labels.
The team notes that cosmetics and personal products are not well regulated in the US - likely due to a lack of data regarding exposure health effects.
Medical News Today recently reported on a study that suggested a certain phthalate found in food packaging could lead to weight gain, for example.
"We know enough to be concerned about teen girls' exposure to these chemicals," says Harley. "Sometimes it's worth taking a precautionary approach, especially if there are easy changes people can make in the products they buy."
The researchers conclude their investigation by writing:
"This study demonstrates that techniques available to consumers, such as choosing personal care products that are labelled to be free of phthalates, parabens, triclosan and BP-3 can reduce personal exposure to possible endocrine-disrupting chemicals."