Could the way you clean between your teeth be associated with your mental health?
A 2026 study published in BMC Oral Health found that US adults who reported cleaning between their teeth more frequently were less likely to screen positive for depression. However, the findings show an association, not proof that interdental cleaning prevents or treats depression.
The study examined data from five cycles of the US National Health and Nutrition Examination Survey (NHANES) from 2009 to 2018. Researchers analyzed whether the frequency of interdental cleaning was associated with depressive symptoms after accounting for a range of demographic, socioeconomic, lifestyle and health factors.
What Did the Study Find?
The study found that more frequent interdental cleaning was associated with lower odds of screening positive for depression.
Among 49,693 potential participants, 17,250 had complete data for the exposure, outcome and covariates included in the analysis. About 8% of participants screened positive for depression.
The researchers reported that:
- Each additional day of interdental cleaning per week was associated with 4.6% lower odds of depression.
- Participants who cleaned between their teeth on at least five days per week had 26.5% lower odds of screening positive for depression compared with those who reported no interdental cleaning.
- Cleaning between the teeth on one to four days per week was not statistically significant after full adjustment.
- Participants who cleaned more frequently also had slightly lower PHQ-9 depression scores.
The study used an odds ratio of 0.954 for each additional cleaning day, with a 95% confidence interval of 0.931 to 0.978.
Was the Study About Flossing?
Not exactly.
The study is sometimes described as research into dental floss use, but participants were asked how many days per week they used dental floss or another device to clean between their teeth.
Therefore, the broader term interdental cleaning is more accurate when describing the exposure.
Interdental cleaning can include dental floss and other devices designed to clean the spaces between teeth. ICPA Health has also discussed the differences between floss and interdental brushes and how the appropriate method can depend on factors such as interdental space and periodontal status.
How Was Depression Measured?
The researchers used the Patient Health Questionnaire-9 (PHQ-9) to assess depressive symptoms.
A PHQ-9 score of 10 or higher was used to classify participants as screening positive for depression.
This distinction is important.
A positive PHQ-9 screening result does not mean that a person has received a clinical diagnosis of depression. The questionnaire identifies people who may have clinically significant depressive symptoms and may require further assessment.
Does Interdental Cleaning Prevent Depression?
No. The study does not establish that interdental cleaning prevents or treats depression.
The research was cross-sectional, meaning that interdental cleaning behaviour and depressive symptoms were assessed within the same survey period.
Because of this study design, researchers cannot determine:
- Whether interdental cleaning came before depressive symptoms
- Whether depression affected a person's oral hygiene habits
- Whether another factor influenced both behaviours
- Whether increasing interdental cleaning would reduce the risk of depression
This is an important distinction between association and causation.
For example, a person experiencing depression may have less energy or motivation for everyday self-care, including oral hygiene. In that situation, depressive symptoms could contribute to less frequent interdental cleaning rather than the reverse.
Why Might Oral Health and Mental Health Be Connected?
There are several possible explanations for the association, but the study does not prove any particular mechanism.
Periodontal Health and Inflammation
Regular interdental cleaning can help remove plaque and debris from areas that a toothbrush may not adequately reach. Better oral hygiene may support periodontal health.
ICPA Health has previously examined the role of interdental cleaning in periodontal health in its article on interdental cleaning and periodontal health.
Researchers have also considered whether inflammatory processes could be one pathway connecting oral and mental health. However, this study cannot establish that reduced inflammation explains the observed association.
Oral Comfort and Nutrition
Poor oral health can affect comfort when eating and may influence food choices or dietary patterns. Better oral health could therefore contribute indirectly to general wellbeing.
Social Confidence
Oral health can influence factors such as breath, appearance and comfort when interacting with other people. These factors may have implications for social wellbeing, although they were not established as causal pathways in this study.
Health Behaviours and Socioeconomic Factors
Frequent interdental cleaning may also be a marker of broader health behaviours.
People who clean between their teeth regularly may be more likely to have access to dental care, maintain other healthy habits, have higher health literacy or have greater access to healthcare.
Although the researchers adjusted for multiple demographic, socioeconomic, lifestyle and health variables, residual or unmeasured confounding cannot be ruled out.
What Are the Main Limitations of the Study?
The findings are interesting, but they need to be interpreted within the study's limitations.
1. It Was a Cross-Sectional Study
The study cannot establish cause and effect or determine which behaviour came first.
2. Oral Hygiene Behaviour Was Self-Reported
Participants reported how frequently they cleaned between their teeth. Self-reported behaviours can be affected by recall or reporting bias.
3. Depression Was Based on Screening
The PHQ-9 was used to identify participants who screened positive for depression. This is not equivalent to a confirmed clinical diagnosis.
4. Complete-Case Analysis May Introduce Bias
Of the 49,693 potential participants, 17,250 had the exposure, outcome and covariate information required for the analysis. Restricting the analysis to participants with complete data can potentially introduce selection bias.
5. Unmeasured Confounding May Remain
Even after statistical adjustment, factors that were not measured or adequately captured may have influenced the results.
6. The Findings May Not Apply to Everyone
The analysis involved non-institutionalized adults in the United States. The results may not necessarily apply to institutionalized populations, clinical populations or people living in other countries.
What Does This Mean for Dental Professionals?
The findings do not change the basic reason for recommending interdental cleaning: maintaining good oral health.
Dental professionals can continue recommending appropriate interdental cleaning based on a patient's oral health needs, preferences and ability to use different interdental cleaning methods.
For patients who want to learn more about interdental cleaning, ICPA Health also provides practical guidance on how to use interdental brushes the right way.
The study may, however, support a broader approach to conversations about oral health and wellbeing.
If a patient shows a noticeable decline in self-care, including oral hygiene, a compassionate conversation may be appropriate. Where clinically indicated, dental professionals can consider appropriate screening, support or referral.
The key message is not that flossing is an antidepressant.
Rather, oral hygiene behaviours may be one part of the broader relationship between oral health and overall health, and the findings highlight the need for further research.
What Should Patients Take Away From the Research?
If you already clean between your teeth, there is no reason to stop based on this study.
If you do not, interdental cleaning can still be an important part of maintaining oral health when recommended as part of your dental care routine.
ICPA Health has previously covered how to floss your teeth correctly and the importance of cleaning areas that a toothbrush may not adequately reach.
However, interdental cleaning should not be viewed as a treatment for depression.
Depression is a serious mental health condition that may require professional assessment and treatment. Changes in oral hygiene habits should not be used to diagnose depression on their own.
Frequently Asked Questions
Is Flossing Linked to Depression?
A 2026 study published in BMC Oral Health found that more frequent interdental cleaning was associated with lower odds of screening positive for depression among US adults. However, the study does not prove that flossing or interdental cleaning prevents or treats depression.
Can Flossing Reduce the Risk of Depression?
The study cannot answer this question definitively. It found an association between more frequent interdental cleaning and lower odds of a positive depression screening result, but its cross-sectional design cannot establish causation.
What Is Interdental Cleaning?
Interdental cleaning refers to cleaning the spaces between the teeth. It can involve dental floss or other interdental cleaning devices.
How Was Depression Assessed in the Study?
Depressive symptoms were assessed using the PHQ-9. A score of 10 or higher was used to classify participants as screening positive for depression. This is a screening measure and not the same as a confirmed clinical diagnosis.
How Often Did Participants Clean Between Their Teeth?
Participants reported how many days per week they used dental floss or another device to clean between their teeth. Cleaning on five or more days per week was associated with lower odds of screening positive for depression compared with no interdental cleaning.
Does This Study Prove That Poor Oral Hygiene Causes Depression?
No. The study found an association, but it does not establish that poor oral hygiene causes depression. Depression could also influence self-care behaviours, and other factors may contribute to both oral hygiene and mental health.
Should Interdental Cleaning Be Used to Treat Depression?
No. Interdental cleaning should not be considered a treatment for depression. It remains an oral-health practice, while depression should be assessed and treated by appropriate healthcare professionals.
The Bottom Line
A population-based analysis published in BMC Oral Health found that more frequent interdental cleaning was associated with lower odds of screening positive for depression.
However, the finding should not be interpreted as evidence that flossing prevents or treats depression. The study was cross-sectional, relied partly on self-reported information, used depression screening rather than clinical diagnosis, and cannot rule out reverse causation or unmeasured confounding.
For dental teams, the practical message remains straightforward: recommend appropriate interdental cleaning for oral-health reasons, while remaining attentive to broader changes in a patient's wellbeing and self-care.
The relationship between oral health and mental health is complex. This study provides an interesting association, but prospective research is needed to determine whether there is a causal relationship between interdental cleaning, oral health and depression.
Reference
Zheng Z, Wu J, Zhang Y, Yu P, Li K, Zhang X, Xiang R. Association between dental floss use and depression: a population-based study. BMC Oral Health. 2026 Jul 8. doi: 10.1186/s12903-026-08908-0. Epub ahead of print. PMID: 42415065.
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