Bacteria from our toilets, as well as viruses and fungi that cause mouth infections, can thrive on our toothbrushes. However, there are many ways to keep your toothbrush clean.
Your toothbrush may have turned into a miniature ecosystem teeming with germs. The bristles become like a dry scrubland, which temporarily transforms into a nutrient-rich wetland every day when soaked in water. Among the tall plastic stalks and their bristled tops, millions of microorganisms thrive and multiply.
In general, your toothbrush is home to between 1 and 12 million bacteria and fungi belonging to hundreds of different species. It also harbors countless viruses. These microorganisms form biological films on the surface of your toothbrush or penetrate into the cracks and crevices of the worn bristles.
The water, saliva, skin cells, and traces of food that come from our mouths every day provide these microorganisms with everything they need to thrive. Occasionally, other microbes from nearby sources-such as when cleaning the toilet or opening a window-join them as well.
Since we brush our teeth twice a day using a toothbrush filled with microorganisms, those microbes can easily enter our mouths. Therefore, we should pay more attention to how clean our toothbrush really is.
What lives on our toothbrushes, what dangers these microorganisms pose, and how we should properly clean our toothbrushes-these questions have prompted dentists and medical researchers to investigate further.
Where do the microorganisms come from?
The microorganisms on a toothbrush mainly come from three sources, says Mark-Kevin Zin, a microbiologist at the Rhine-Waal University of Applied Sciences in Germany, who has studied microbial contamination on toothbrushes. They originate from the user’s mouth, their skin, and the environment in which the toothbrush is kept.
Not only in the toothbrushes we use, but even in new toothbrushes purchased from stores, there may be various microorganisms present before we start using them. For example, a study of 40 new toothbrushes purchased from different manufacturers in stores in Brazil found that half of them were already contaminated with various bacteria.
Fortunately, most of the microorganisms found on the toothbrushes we use are not highly harmful. Surprisingly, our mouths themselves harbor many microorganisms. Each time we put the toothbrush in our mouth and brush, the toothbrush removes microorganisms such as Nurodia tenocariosa, Streptococcaceae mites, and Actinomyces bacteria that live in our mouths.
Some of these microorganisms are beneficial to our health and help protect us from harmful bacteria that cause tooth decay. However, among them, there are also microorganisms that can cause harm to us.
Harmful bacteria
The most important among these are Streptococci and Staphylococci, which cause tooth decay, says Vinicius Petrassi, a professor of dentistry at the University of São Paulo in Brazil. Some of these bacteria can cause inflammation in our gums, which is called periodontal disease.
Researchers have also identified bacteria and fungi living on used toothbrushes. Organisms commonly associated with stomach infections and food poisoning, such as Escherichia coli, Pseudomonas aeruginosa, and Enterobacter, have been found on toothbrushes.
In addition, studies have detected pathogens commonly responsible for hospital infections, such as Klebsiella pneumoniae and Candida yeast.
These microorganisms can come from the water we use to clean our toothbrushes, from our hands, and from other parts of the environment. Nevertheless, your bathroom may be a particularly favourable environment for harmful bacteria to develop.
Bathrooms are warm and humid places where fine water droplets, aerosols carrying bacteria and viruses, continuously spread through the air. This increases the chances of contamination for dental care items kept in the bathroom, says Zin.
Typically, our bathrooms also contain the toilets, and that is where we keep our toothbrushes. That’s why toothbrushes kept in the bathroom become filled with microorganisms.
Toilet cleaning
Every time the toilet is flushed, tiny water droplets and microscopic fecal particles can spray into the air up to 1.5 meters (5 feet) around it. These droplets may contain bacteria and infectious viruses, such as those that cause fever, COVID-19, and norovirus, which leads to stomach upset.
If you keep your toothbrush in the bathroom near the toilet, it can become contaminated with these contents, increasing the risk that infectious microorganisms will settle directly on the brush. However, closing the toilet lid when flushing and rinsing the toilet can help reduce this risk.
Furthermore, in shared bathrooms, the risk may be even higher. A study conducted at a university found that 60% of toothbrushes kept in public bathrooms were contaminated with bacteria found in feces, and there was a high likelihood that microorganisms on one person’s toothbrush came from another person.
Erika Hartman, an associate professor of engineering at Northwestern University in Illinois, USA, who studies how microorganisms survive in real-world environments, says that the microorganisms found in bathrooms are not actually very concerning.
In research conducted by her team on 34 toothbrushes sent by the public, they did not find as many fecal-related bacteria as expected. She points to studies from Illinois showing that many gut-related microorganisms do not survive long once exposed to air.
I don’t think most people face health problems from their toothbrushes, she says.
However, some studies show that viruses such as influenza and coronavirus can survive on toothbrushes for several hours, and herpes simplex virus-1, which causes cold sores, can live for up to 48 hours. This indicates the possibility of disease transmission.
For this reason, public health advice recommends not sharing dental care items. If you store more than one toothbrush together, especially, they should not be kept alongside those of people who do not live with you, as warned by public health organizations.
However, Hartman says this is not a major problem for people living in the same household. People who live together share a higher proportion of the microorganisms in their mouths compared to those who do not,” she explains. “I believe this can happen not only through direct ways like kissing but also indirectly, such as by keeping toothbrushes close to each other. (It is also noteworthy that dog owners often share many of the microorganisms present in their pets.)
In fact, some of the viruses found on toothbrushes can actually be beneficial to us. Hartman and her team discovered that toothbrushes harbor thriving communities of viruses called bacteriophages, which infect bacteria rather than humans and help control their numbers.
Zin, who acknowledges that the risk posed by pathogens is minimal in most cases, notes that people with weakened immune systems are more susceptible to infections. Along with other studies that have sequenced bacterial DNA during tooth brushing, Zin’s research has found that at least some of these bacteria carry genes that help them resist antimicrobial agents.
This means that if they cause infections, treating them would be difficult. However, Zin points out that in his research, these genes were present in “relatively low amounts,” so they pose only a “moderate concern from a public health perspective.”
However, a study conducted among students in Italy during tooth brushing found that all of them harbored bacteria resistant to multiple drugs. Some toothbrushes are marketed as containing antimicrobial treatments that claim to keep the bacteria living on your toothbrush under control. However, most studies show that these antimicrobial treatments only moderately help reduce the number of bacteria on your brush and may also contribute to the increase of antimicrobial-resistant strains.
A simple way to reduce the microorganisms on your toothbrush is to let it air dry upright at room temperature after use. Many viruses, including influenza and coronavirus, cannot survive without moisture. Bacteria that play a major role in tooth decay, such as Streptococcus mutans, can survive on toothbrushes for up to eight hours and begin to die after 12 hours.
The American Dental Association and the Centers for Disease Control and Prevention recommend not covering the bristle area of the toothbrush or storing it in closed containers because this promotes the growth of microorganisms.
How to clean your toothbrush?
Methods to disinfect dental care items include using ultraviolet light, placing them in a dishwasher or microwave, drying them with a hairdryer, or soaking them in a glass of whisky. Microwaving is often found to be very effective, but there is a chance it may melt or damage your toothbrush.
The toothpaste you use may also have antimicrobial properties that help reduce the number of microorganisms growing on your toothbrush. Rinsing your toothbrush thoroughly with water helps remove some bacteria, but many bacteria still remain.
Some researchers recommend rinsing the toothbrush in a solution containing 1% vinegar as one of the best ways to reduce bacteria. However, your results may vary the next time you try it. Therefore, soaking the toothbrush in an antimicrobial mouthwash for five to ten minutes can also be beneficial. Petrassi recommends disinfecting toothbrushes with mouthwashes containing 0.12% chlorhexidine or 0.05% cetylpyridinium chloride.
However, some researchers take a different approach and suggest that toothpaste can actually encourage bacterial growth. Old toothbrushes that have been used for a long time contain the moisture and nutrients needed for bacteria to grow. This is one reason why dental health organizations like the American Dental Association recommend replacing your toothbrush every three months. This recommendation is especially important for people with weakened immune systems. Zin’s research also found that bacterial loads on toothbrushes peak after about 12 weeks of use.
However, some researchers are taking a different approach, suggesting that bacteria growth can actually be encouraged by toothpaste. Probiotic toothpastes may be used to promote the growth of certain “friendly” bacteria known to be beneficial for oral health.
For example, Streptococcus salivarius is known to suppress harmful bacteria and help fight plaque. This is being tested by a company in New Zealand. Another example is Limosilactobacillus reuteri, which strongly competes against Streptococcus mutans, a bacteria that contributes to tooth decay. Probiotic toothpastes or bioactive bristle materials may offer innovative ways to promote a healthy microbial balance on toothbrushes,” says Jin. However, he warns that much more research is still needed in this area. If you carefully pay attention to your toothbrush in your bathroom, it is important to know when it’s time to replace it. You can also move it farther away from your toilet.