Before you freshen up with anti-bacterial mouthwash after a heavy sweat session, ask yourself whether it’s really necessary. Working out commonly leads to a drop in blood pressure, but using an anti-bacterial mouthwash after training significantly reduces this benefit, according to a study published in Free Radical Biology and Medicine (2019; 143, 252–59). Rinsing with water, in contrast, does not affect blood pressure.

Researchers from the University of Plymouth, England, and various institutions in Spain conducted a study to evaluate the role of mouth bacteria in converting salivary nitrites into nitrate, a chemical that helps to keep blood vessels dilated, leading to lower blood pressure after exercise.

Investigators recruited 23 healthy adults to run on a treadmill and rinse their mouths 30, 60 and 90 minutes after running. Blood pressure was monitored. Data analysis showed that the anti-bacterial mouthwash reduced exercise’s lowering effect on blood pressure by more than 60% during the first hour of recovery and eliminated the benefit within 2 hours after exercise.

Lead study author Craig Cutler, a PhD student in dietetics at the University of Plymouth, said, “These findings show that nitrite synthesis by oral bacteria is hugely important in kick-starting how our bodies react to exercise over the first period of recovery, promoting lower blood pressure and greater muscle oxygenation.”