Millions of bacteria thrive on toothbrushes, research reveals

Toothbrushes harbour between 1-12 million bacteria and fungi from hundreds of different species, with some capable of causing oral disease and infections, scientists have found, according to a BBC report.

Microbiologists at Rhine-Waal University of Applied Sciences in Germany have identified that used toothbrushes form biological films on their surfaces, creating ideal conditions for microbes to thrive.

“The microbes on toothbrushes primarily originate from three sources – the user’s mouth, their skin and the environment where the toothbrush is kept,” said Marc-Kevin Zinn, lead researcher on toothbrush contamination.

While most bacteria found on brushes are harmless mouth residents, researchers have identified potentially dangerous pathogens including Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae on some samples.

Research from multiple institutions has revealed that bathroom environments contribute significantly to contamination, particularly when toothbrushes are stored near toilets.

“Every time you flush the toilet, a plume of tiny droplets containing water and faeces are thrown up to 1.5 metres into the air,” said Vinicius Pedrazzi, professor of dentistry at the University of São Paulo, Brazil. These aerosols can deposit bacteria and viruses onto nearby surfaces, including toothbrushes.

Studies have shown that viruses such as influenza and coronaviruses can survive on toothbrushes for several hours, while herpes simplex virus-1, which causes cold sores, may persist for up to 48 hours.

A study of student toothbrushes in communal bathrooms found 60% were contaminated with faecal bacteria, prompting public health officials to recommend not storing brushes in close proximity to one another.

Erica Hartmann, associate professor of engineering at Northwestern University in Illinois, takes a more measured view. “I don’t think most people are getting sick from their toothbrush,” she said, noting that many gut-associated microbes don’t survive long when exposed to air.

Experts recommend allowing brushes to air dry upright after use, as many bacteria begin dying off after 12 hours in dry conditions. Storing brushes in closed containers is discouraged as this environment can promote microbial growth.

Research indicates that bacterial loads peak after approximately 12 weeks of use, supporting dental health organisations’ recommendations to replace toothbrushes every three months.

For those concerned about contamination, solutions including soaking brush heads in antiseptic mouthwash or diluted vinegar can reduce bacterial counts, though researchers are also exploring probiotic toothpastes designed to encourage beneficial bacterial growth.