People who brush their teeth with their right hand might be cleaning the left side of their mouth differently, and this could be why a certain inflammatory protein is lower on that side — especially if they're taking fish oil supplements.

We analyzed one assertion about handedness and gum inflammation in people taking EPA and DHA supplements, and it supports the idea that right-handed individuals may clean the left side of their mouth differently while brushing, which could relate to lower levels of a specific inflammatory protein on that side — particularly when they’re taking fish oil supplements [1]. What we’ve found so far is limited to this single assertion, with no studies contradicting it. The claim suggests a possible link between hand preference, brushing habits, and localized changes in gum inflammation markers, with fish oil supplements possibly playing a role. But we don’t know how strong this connection is, or whether the difference in protein levels is meaningful for overall oral health. We also don’t know if this pattern holds for left-handed people, or if the effect is consistent across different populations, brushing techniques, or supplement doses. The evidence doesn’t explain why fish oil might interact with brushing side preference, nor does it show whether this difference leads to better or worse gum health over time. There’s no data on how often people brush, how long they brush each side, or whether the inflammatory protein measured is a direct indicator of gum disease. Without more studies, we can’t say whether this is a real biological effect or just a coincidence tied to how people move their hands while brushing. The evidence we’ve reviewed so far doesn’t rule out the possibility, but it also doesn’t confirm it. Practical takeaway: If you take fish oil and notice one side of your mouth feels different, it might be worth paying extra attention to your brushing technique on both sides — but don’t assume handedness is the cause.