In an experiment led by scientists from the UK and Spain, researchers found that the simple act of using mouthwash after exercising can reduce one of the benefits of exercise: lowering blood pressure .

When you exercise, your blood vessels open in response to the production of nitric oxide , which increases the diameter of blood vessels. This process is called vasodilation , and it increases blood flow circulation to active muscles.

For a long time, researchers thought this only happened during exercise, but in more recent years, evidence has shown that circulation stays high (meaning blood pressure is lowered) even after exercise – thanks to how bacteria interact with a compound called nitrate, which forms when nitric oxide degrades.

"Research over the last decade has shown that nitrate can be absorbed in the salivary glands and excreted with saliva in the mouth," explains physiology specialist Raul Bescos from Plymouth University.

"Some species of bacteria in the mouth can use nitrate and convert into nitrite – a very important molecule that can enhance the production of nitric oxide in the body."

Once nitrite is produced and swallowed with saliva, it becomes absorbed into blood circulation and reduces back to nitric oxide, which keeps blood vessels wide and lowers blood pressure.

But according to this small study, it looks like this biological mechanism can be significantly interrupted if anti-bacterial mouthwash gets added into the post-exercise mix.

In an experiment, 23 healthy adults ran on a treadmill for 30 minutes. After the workout, the participants were asked to rinse their mouth with either an antibacterial mouthwash or a mint-flavoured placebo.

These mouth rinses occurred immediately after the exercise, and also at 30, 60, and 90 minutes after.

At the end of the monitoring window, two hours after the treadmill session, the mouthwash group showed no sign of blood pressure reduction stemming from the exercise, whereas the placebo group still showed a significant reduction compared to their pre-exercise values.

"This is the first evidence showing that the nitrate-reducing activity of oral bacteria is a key mechanism to induce the acute cardiovascular response to exercise during the recovery period in healthy individuals," the authors explained in their paper .

While it's only a small study, it serves as an important reminder of how not all bacteria are necessarily bad for us – and that ingesting antibacterial chemicals that indiscriminately terminate mouth-dwelling microbes could hamper important biological processes necessary for good health.