A chemical contained in some brands of toothpaste accumulates in toothbrushes over time and is then released into a person’s mouth when they switch to a different type of toothpaste, according to researchers at University of Massachusetts Amherst.

A team of environmental chemists reported in the journal “Environmental Science and Technology” that triclosan — an antibacterial agent that has been banned from other products — builds up in the bristles and other soft parts of toothbrushes, the university said in a statement.

Triclosan is only found in antibacterial toothpastes, the university said. When users switch to a different toothpaste brand that does not contain triclosan, it is released into the user’s mouth with every brush.


The team, as well as the US Food and Drug Administration, does not consider oral exposure to toothpastes that contain triclosan a health risk, but triclosan is banned in other personal products such as soaps, gels, and sanitary wipes, the university said.

“We ... recommend being aware of the uncontrolled accumulation and release behavior of this chemical, and potential unwanted exposure when users decide to switch to other regular toothpastes,” Baoshan Xing, the chemistry professor who leads the team, said in the statement.

There is evidence that triclosan does have health benefits, according to the FDA’s consumer updates page on the ingredient. For instance, data from a 1997 test on triclosan in Colgate toothpaste revealed it could help prevent gingivitis.

Still, UMass researchers say there are still safety questions about the ingredient. The FDA warns that some studies of triclosan on animals show exposure to the ingredient is associated with low levels of thyroid hormones, and others suggest it could help bacterial diseases resist antibiotics, although the information made available by those studies is not substantial enough to definitively assess health risks for humans.


“We just want to make people aware that certain toothpaste chemicals can accumulate to substantial levels as they brush, and consumers can make up their own minds,” Xing said in the statement.

The researchers used an automated brushing simulator and artificial saliva to simulate brushing teeth for two minutes twice a day for three months, the university said.

They tested 22 types of toothbrushes and toothpastes with and without triclosan, the university said. Over one third of the brushes absorbed significant amounts of the ingredient, with toothbrushes made of soft polymer accumulating the most.

When those toothbrushes were used with nontriclosan toothpastes, the agent was gradually released, the university said.

Xing and his team said the accumulation and subsequent release of triclosan is not an issue limited to toothbrushes.

“On a larger scale, our study also raises broad questions on the general design of consumer products . . . that are regularly exposed to chemicals during use, particularly those used in personal care products,” they said in the statement.

Alyssa Meyers can be reached at alyssa.meyers@globe.com. Follow her on Twitter @ameyers_.