Bacteria from our toilets, the cold sore virus and thrush-causing yeast can thrive on our toothbrushes. But there are ways to keep your toothbrush a little cleaner.

Your toothbrush is a disgusting miniature ecosystem. Its fraying bristles form an arid scrubland that each day is temporarily flooded, transforming it into a wetland awash with nutrients. Thriving among the thickets of towering plastic stalks are millions of organisms.

Right now your toothbrush is home to something like 1-12 million bacteria and fungi belonging to hundreds of different species, alongside countless viruses. They form biological films on the exposed surfaces of your brush, or worm their way into the fractured stalks of ageing bristles. A daily influx of water, saliva, skin cells and traces of food from our mouths give these microbes all they need to thrive. Every so often, they are joined by a shower of other microorganisms that arrive with the flush of a nearby toilet or opening of a window.

And twice a day you put this delightful cocktail into your mouth to give it a good stir around.

So, should you be more concerned about how clean your toothbrush is?

It's a question that has been troubling dentists and doctors for years, prompting them to examine just what is living on our toothbrushes, what risks those microbes pose and how we should be cleaning our tooth-scrubbing implements. (You can also learn more about how to properly brush your teeth accordng to science in this article by Martha Henriques.)

"The microbes on toothbrushes primarily originate from three sources," says Marc-Kevin Zinn, a microbiologist at Rhine-Waal University of Applied Sciences in Germany, who has studied the microbial contamination of toothbrushes. These are the user's mouth, their skin and the environment where the toothbrush is kept.

But before we even use a toothbrush for the first time it can carry its own community of microbes. A study of 40 new toothbrushes from different manufacturers bought from stores in Brazil, for example, found half were already contaminated with a variety of bacteria.

Fortunately, most of the microbes found on our used toothbrushes are fairly harmless. The majority come, perhaps unsurprisingly, from our own mouths. Each time we pop the brush into our oral cavity, the bristles sweep up microbes such as Rothia denocariosa, Streptococcaceae mitis and members of the Actinomyces bacteria – all normally benign residents of our mouths. Some of those clinging to the bristles and toothbrush head can even be beneficial for our health, helping to protect us against other microbes that cause tooth decay.

But lurking amongst them are hitchhikers that do mean us harm.

"The most important are Streptococci and Staphylococci, which cause tooth decay," says Vinicius Pedrazzi, a professor of dentistry at the University of São Paulo in Brazil. Others can cause inflammation in our gums, known as periodontal disease.

Researchers have also found bacteria and fungi living on used toothbrushes that have no right to be there – organisms more commonly associated with stomach infections and food poisoning such as Escherichia coli, Pseudomonas aeruginosa, and Enterobacteria. Studies have also identified pathogens like Klebsiella pneumoniae – a common cause of hospital-acquired infections – and Candida yeasts, which can........

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