FACT CHECK: Does not changing your toothbrush make you prone to cancer?

CLAIM:

Not replacing a toothbrush every three months can allow harmful bacteria to accumulate and may increase the risk of serious diseases, including cancer. The reel suggests that because most people use the same toothbrush for a year, they may unknowingly be putting their health at risk.

FACT:

There is no evidence that using the same toothbrush for longer than three months causes cancer. While old toothbrushes can accumulate bacteria and become less effective at cleaning teeth, studies and experts indicate that the link to cancer, if any, is indirect and mediated through poor oral hygiene and chronic inflammation rather than the toothbrush itself.

In a recent Instagram reel posted by ‘Neer Yaduvanshi’, who has 17.6k followers on Instagram, concerns have been raised about the health risks associated with not replacing toothbrushes regularly. The video suggests that failing to change a toothbrush every three months, as recommended on most toothbrush packaging, could expose people to harmful bacteria and potentially increase their risk of serious illnesses, including cancer.

In the reel, a clip of Dr Tarang Krishna is featured, in which he points out that most people ignore the instructions printed on toothbrush packets. Citing a study, he claims that “95 per cent of people in India change their toothbrush once a year.” He urges viewers to check a new toothbrush packet and says, “It will say, please discard it in 3 months.” 

Emphasising that the recommendation is widely overlooked, he asks, “How many people change their toothbrush? Have you ever seen a toothbrush packet? There is a guideline written on it. Everyone has ignored it.” The reel implies that prolonged use of the same toothbrush may have serious health consequences and has sparked concern among viewers about whether this common habit could make them more prone to diseases such as cancer. 

Does not changing your toothbrush make you prone to cancer? 

While studies show that toothbrushes can accumulate bacteria over time, there is no evidence that using the same toothbrush for longer than three months causes cancer. Research instead suggests that good oral hygiene and regular toothbrushing are associated with lower cancer risk, and dental health organisations recommend replacing toothbrushes every three to four months, primarily to maintain effective oral hygiene.  

A 2012 review published in the American Journal of Infection Control examined the existing literature on toothbrush contamination and found that toothbrushes used by both healthy individuals and those with oral diseases can become contaminated with bacteria originating from dental plaque, the environment, or the brush itself. However, the authors noted that “there are no studies that specifically examine toothbrush contamination and disease transmission,” highlighting that the presence of microbes does not automatically translate into disease. 

Subsequent research has reached similar conclusions. A 2020 study that analysed the microbiome of used toothbrushes found that they “harbour various microorganisms” and that the composition of these microbes changes depending on how long the toothbrush has been used and the age of the user. The researchers identified bacterial counts ranging from 1.42 × 10⁶ to 1.19 × 10⁷ colony-forming units per toothbrush, but found relatively low frequencies of antibiotic resistance genes and did not link these microorganisms to cancer. 

Likewise, a 2021 study investigating 103 used toothbrushes reported that 97% were contaminated with microbes, including enteric bacteria and Candida. The authors concluded that used toothbrushes are “heavily contaminated” and that the presence of potentially pathogenic microorganisms constitutes a “potential health risk.” Importantly, the study also found that microbial loads were largely established within the first three months and did not continue increasing substantially with prolonged use. The study did not examine cancer risk. 

While no studies have linked old toothbrushes themselves to cancer, several epidemiological studies have explored the broader relationship between oral hygiene and cancer. A 2021 study involving more than 20,000 Japanese dentists found that infrequent toothbrushing - less than twice a day - was associated with a higher risk of upper aerodigestive tract cancers. The researchers reported that “infrequent toothbrushing (<2 times/day) was significantly associated with increased risk of UADT cancer.” However, the study focused on brushing frequency rather than how often toothbrushes are replaced. 

Similarly, a 2022 analysis from the China Kadoorie Biobank, which followed more than 5.1 lakh adults, found that poor oral health, defined by rarely brushing teeth and frequent gum bleeding, was associated with a modest increase in overall cancer incidence and mortality. The association was particularly evident for cancers of the digestive system, including stomach, oesophageal and liver cancers. The authors concluded that “promotion of oral health in the general population… could have valuable public health significance in preventing major systemic diseases.” 

More recently, a 2024 Japanese study examining data from 32,000 individuals found a significant association between toothbrushing habits and cancer prevalence. The researchers suggested that “daily toothbrushing is important for preventing cancer, thereby highlighting the importance of oral health in relation to cancer risk,” although they acknowledged that the cross-sectional nature of the study made it difficult to establish a causal relationship. They also noted that oral hygiene habits often reflect broader healthy lifestyle behaviours. 

Professional bodies echo these findings. The American Oncology Institute notes that the World Health Organisation (WHO) recognises the importance of oral hygiene in preventing not only dental problems but also certain systemic diseases. It advises that “regular brushing, flossing, and dental check-ups are recommended to maintain oral health and prevent periodontal disease,” and recommends replacing toothbrushes “every three to four months or sooner if the bristles are frayed.”  

What experts recommend?

Dr Manikandan Venkatasubramaniyan, Senior Consultant, Surgical Oncology, MGM Cancer Institute, Chennai, said that using the same toothbrush for prolonged periods or sharing it with others may indirectly contribute to cancer risk by promoting chronic oral inflammation and facilitating the transmission of certain cancer-associated viruses. However, he emphasised that the risk is indirect and mediated through poor oral health rather than the toothbrush itself. 

Referring to existing evidence, he noted that some studies have linked oral bacteria such as Fusobacterium nucleatum to colorectal cancer. “When you see the scientific evidence, there are few published papers which say that some oral bacteria like Fusobacterium nucleatum can travel through bleeding gums into the bloodstream, and that has been linked to colorectal cancers,” he said. 

According to Dr Manikandan, old and frayed toothbrushes become less effective at removing plaque, which can lead to periodontitis and persistent inflammation. “This chronic oral inflammation is a known catalyst that can trigger cancer cell mutations,” he explained. He also cautioned against sharing toothbrushes, noting that saliva and blood contamination could facilitate the spread of human papillomavirus (HPV), certain strains of which are associated with oral, oesophageal and cervical cancers. 

He further pointed to recommendations from dental and medical bodies on maintaining oral hygiene. “Swap your manual brush or electric brush head at least every 90 days. Replace it sooner if the bristles become frayed or flared,” he advised. He also recommended discarding toothbrushes after recovering from infectious illnesses, never sharing toothbrushes, storing them upright in open air to allow complete drying, and avoiding enclosed caps or containers where multiple toothbrushes come into contact. 

“When you follow these recommendations, you can maintain good oral hygiene,” he added. 

Dr Anand S, Specialist in Oral Medicine and Radiology at MIDAC Dental Centre, Kozhikode, agreed that toothbrushes should ideally be replaced every three to four months, but stressed that the recommendation is aimed at maintaining effective oral hygiene rather than preventing cancer. He explained that over time, the nylon bristles become bent and split, reducing the brush's ability to clean teeth properly. In addition, bacteria from the mouth can accumulate on the toothbrush, although this does not translate into a cancer risk. 

“People should change their brush every three to four months because the bristles wear out and the cleaning efficiency decreases,” he said. “Microbial colonisation can occur, but it’s not going to cause cancer directly. It just means you cannot clean your teeth as effectively as you are supposed to.” 

Dr Anand emphasised that there is no evidence linking prolonged use of the same toothbrush to cancer. “I don’t think people should be made scared by telling them ‘cancer’ and all. There’s nothing related to cancer,” he said, adding that while some people may stretch usage to six months, dentists generally recommend replacing toothbrushes every three to four months. 

This story is done in collaboration with First Check, which is the health journalism vertical of DataLEADS