Triclosan has been banned in many products, but not in toothpaste. Researchers say this chemical can accumulate on your toothbrush and cause health problems.

A new law has banned an antibacterial chemical in many household products.

But not in toothpaste.

Now, new research shows that this substance accumulates in toothbrush bristles.

And that is raising questions about the risks of long-term exposure and possible health impacts.

Triclosan has been shown to interfere with hormones, kill some aquatic life, and contribute to antibiotic resistance.

But it has also been shown to help reduce plaque, cavities, and inflammation of the gums.

In small concentrations allowed in over-the-counter toothpastes, triclosan is considered safe.

However, a new study has found that over time the chemical is absorbed from toothpastes into the bristles of some toothbrushes.

After 3 months of brushing, more than one-third of brushes tested contained 7 to 12.5 times the amount of triclosan that one would be exposed to from toothpaste during a typical brushing session.

The accumulation itself isn’t necessarily a health risk, said Jie Han, a postdoctoral researcher at the University of Massachusetts Amherst Stockbridge School of Agriculture.

It’s what comes next.

“The subsequent release of these chemicals, which occurs in an unregulated manner, can lead to prolonged and unexpected exposure,” Han told Healthline.

The exposure is greatest during the first few brushes after switching to a triclosan-free toothpaste and continuing to use the same brush, Han said.

The simplest way to reduce your exposure risk would be to throw out your old toothbrush when switching to a new toothpaste.

That, however, only decreases your personal exposure.

The toothbrushes — and the triclosan they’re carrying — have to go somewhere.

Usually that’s to a landfill.

“Because users change their toothbrushes on a regular basis, these can become a sustained source of certain chemicals in the environment that were previously not accounted for,” Han said. “As we found in this study, some of these chemicals can accumulate to substantial amounts after three months of use.”

If that waste is burned, dioxins, a powerful carcinogen, can be released into the air, said Rolf Halden, PhD, director of Arizona State’s Biodesign Center for Environmental Health Engineering.

Even before entering landfills, toothbrush bristles may enter wastewater and expose aquatic life to triclosan.

Halden said the chemical is “one of the top ten pollutants among over a hundred pharmaceuticals and personal care products detectable in U.S. surface water.”

Halden recommends a simple way to reduce exposure.

Avoid toothpastes that contain triclosan unless your physician or dentist recommends it for its potential dental benefits.

Halden, the lead author of a statement on the use of triclosan published this summer, also recommends greater scrutiny of the hazards and supposed benefits of triclosan and increased transparency over its use.

“When you use the chemical, it is mostly ineffective in protecting from germs, and instead actually may increase microbial risks by producing bacteria that are cross-resistant to antibiotics your doctor prescribes to save lives,” Halden said at the time of the release of the Florence Statement on Triclosan and Triclocarban.

That statement also noted that triclosan can increase susceptibility to allergies.

It also is often found in breast milk and has been tied to slower growth of fetuses late in pregnancies.

The statement said there is no evidence of health benefits from the use of triclosan in soaps, although the scientists don’t refute the gum disease-treatment benefits.

The Food and Drug Administration (FDA) rule banning triclosan in many products, including most soaps and body washes, was announced in September 2016 and went into effect this September.

But its scope is limited by the agency’s reach.

Carpets, toys, clothing, and cookware — in addition to toothpastes — are not covered by the rule.

To avoid triclosan, Halden said consumers should be wary when they see claims that a product is antimicrobial or antibacterial.

“As a rule of thumb,” he said, “use of regular soap and water will get the job done without posing undue risks to consumers, whether it’s about washing your hands or keeping your living area tidy.”