Changing toothpastes? Change your toothbrush | Science News for Students

Changing toothpastes? Change your toothbrush

Toothbrushes can absorb an antimicrobial chemical then release it after users switch toothpastes
Jan 19, 2018 — 6:45 am EST
toothpaste on toothbrush
The bristles of your toothbrush can absorb triclosan from toothpaste, a new study shows. Later, that chemical can come out again and expose your mouth.

Some popular toothpastes contain an germ-killing chemical called triclosan. Studies have shown that it may help fight the bacteria behind gum disease. But after the U.S. government banned triclosan from soaps and other cleaning products, many people decided to steer clear of the chemical in other products too. Many switched to triclosan-free toothpastes. A new study has now shown that may not help — unless users also got a new toothbrush. Why? Triclosan can stick around in toothbrushes, exposing people once again after they turn to a new toothpaste.

In 2016, the U.S. Food and Drug Administration banned triclosan and 18 other antiseptic chemicals from use in soaps. There was little evidence that the chemicals actually helped to prevent the spread of germs. What’s more, studies showed they could pose health risks, cause problems in the environment or contribute to antibiotic resistance. Triclosan was thought to do all three.

Yet it wasn’t banned from toothpastes. The reason: Some data showed that it might help fight gum disease. Still, many people switched toothpastes when they realized theirs contained the controversial chemical.

Jie Han and Baoshan Xing are environmental chemists. They work at the University of Massachusetts in Amherst. Their team has studied how various materials absorb different types of chemicals. After the FDA ban, they began to wonder whether triclosan sticks around in toothbrushes.

Brush, brush, brush

To probe that, they teamed up with chemists and engineers in Connecticut and New Zealand. The group chose 22 different types of toothbrushes that are popular in the United States. These ranged from full-sized brushes for adults to pea-sized ones for little kids. The brushes also varied in their features. Some had only nylon bristles. Others also had polishing cups and cheek/tongue cleaners made from a polymer called an elastomer (Ee-LAS-toh-mur). The researchers also bought 21 types of toothpaste. Six of them contained triclosan.

They mixed one part toothpaste with three parts of a chemical mix that mimics saliva. This created a “slurry.” It resembled what develops inside the mouth when brushing your teeth.

The researchers poured the slurry into a straight-sided vial. Then they brushed the inside of that container with the selected toothbrush for two minutes. They repeated this process up to 168 times. That’s equivalent to the number of times a person would use a toothbrush over a three-month period. (Dentists recommend that people get a new toothbrush every three months.)

Then the researchers tested the brushes and mixtures for triclosan. They didn’t want to test every single bristle. And they didn’t have to. They knew how much triclosan had been in the toothpaste applied to each toothbrush. They just subtracted how much ended up in the slurry. This told them how much must have been absorbed by the brushes.

Most brushes absorbed the triclosan from the toothpaste slurry. They accumulated the most during the first few times they were used. But they continued to pick up a little more with each additional use (just not as much as at the beginning).

The total amount that was absorbed depended on the brush. Those with added features generally absorbed much more than those with bristles only. That’s because these “accessories” are made of a different material than the bristles, Han explains. That material is better at absorbing the triclosan.

What goes in may come out

The researchers then looked at what would happen if someone switched to a toothpaste that contained no triclosan. Would the triclosan in that toothbrush now leach out into the mouth from the bristles?

To find out, the group repeated the experiment using brushes from the first experiment that had absorbed triclosan. Now, the only source of the triclosan would be those old brushes. And sure enough, triclosan leached into the slurry after brushing with a triclosan-free toothpaste. It did so again and again after each brushing.

The researchers reported their findings in the November 7, 2017 Environmental Science & Technology.

These data show that switching from a triclosan-containing toothpaste to a brand free of this chemical won’t prevent exposure, says Margaret James. She’s a chemist at the University of Florida in Gainesville. She was not involved with the study. “Unless a new toothbrush is used with the triclosan-free toothpaste,” she says, exposure to the chemical may not go away.

“This may seem wasteful,” Han concedes, but the best way to ensure that this exposure ends is to switch to a new toothbrush any time you switch toothpastes. People also may lower their exposures by choosing to use brushes that have only bristles. “We found these [bristles] accumulate much smaller amounts of triclosan” than other brushes. Another benefit, she notes, is that they also tend to cost less.

Power Words

(more about Power Words)

antibacterial     Having properties that tend to destroy or limit the growth or reproduction of bacteria.

antibiotic     A germ-killing substance, usually prescribed as a medicine (or sometimes as a feed additive to promote the growth of livestock). It does not work against viruses.

antimicrobial     A substance used to kill or inhibit the growth of microbes. This includes naturally derived chemicals, such as many antibiotic medicines. It also includes synthetic chemical products, such as triclosan and triclocarban. Manufacturers have added some antimicrobials — especially triclosan — to a range of sponges, soaps and other household products to deter the growth of germs.

antiseptic     (noun) A chemical, such as alcohol, used to kill germs. (adj.) A surface or environment that it totally germ-free or scrupulously clean. 

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

elastomer    A long, chain-like molecule (polymer) that has rubbery properties. They can generally recover their shape after being stretched a lot. In fact the term is a shortened version of “elastic polymer.” The molecules tend to have a coiled shape. Stretching them straightens out the coils. But they spring back into a coil when the force is taken away.  The primary constituent of rubber is a natural elastomer known as polyisoprene.



Food and Drug Administration (or FDA)     A part of the U.S. Department of Health and Human Services, FDA is charged with overseeing the safety of many products. For instance, it is responsible for making sure drugs are properly labeled, safe and effective; that cosmetics and food supplements are safe and properly labeled; and that tobacco products are regulated.

germ     Any one-celled microorganism, such as a bacterium or fungal species, or a virus particle. Some germs cause disease. Others can promote the health of more complex organisms, including birds and mammals. The health effects of most germs, however, remain unknown.

leach     (in geology and chemistry) The process by which water (often in the form of rain) removes soluble minerals or other chemicals from a solid, such as rock, or from sand, soil, bones, trash or ash.


nylon     A silky material that is made from long, manufactured molecules called polymers. These are long chains of atoms linked together.

resistance     (as in drug resistance) The reduction in the effectiveness of a drug to cure a disease, usually a microbial infection. (as in disease resistance) The ability of an organism to fight off disease. (as in exercise) A type of rather sedentary exercise that relies on the contraction of muscles to build strength in localized tissues. (in physics) Something that keeps a physical material (such as a block of wood, flow of water or air) from moving freely, usually because it provides friction to impede its motion.

risk     The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

triclosan     A germ-killing chemical added to some common products such as hand soaps and sponges.


Journal: J. Han et al. Nylon bristles and elastomers retain centigram levels of triclosan and other chemicals from toothpastes: Accumulation and uncontrolled release. Environmental Science & Technology. Vol. 51, November 7, 2017, p. 12264. doi:10.1021/acs.est.7b02839.