Want to avoid colds, flu, RSV and more? A common habit in Japan might help.
In fact, people have been doing it several times a day for centuries to prevent colds – at school, at home and in the office. It’s completely free: it will only cost you tap water and a few moments of your day.
Research suggests that this may not just be an old wives’ tale or cultural phenomenon.
This is called “ugai”, rinsing your mouth with water. In Japan, it is as common a practice as washing your hands. In fact, gargling is often done during the same bathroom visit.
The idea is that it will dislodge and eliminate harmful microbes before they create an infection.
The researchers tested plain water against no gargling and gargling with a povidone-iodine rinse – an antiseptic sold as Betadine for sore throats in US pharmacies.
They found that gargling with water was significantly more effective than medication and not gargling when it came to keeping people healthy. But other researchers say the benefits aren’t as clear-cut.
Here’s what you need to know.
What the researchers discovered
The researchers divided 387 participants aged 18 to 65 into three groups: one who continued their normal habits without gargling, one who gargled with water three times a day, and one who gargled with diluted povidone-iodine three times a day.
They continued through the cold winter season and many fell ill within two months.
Those who gargled with plain water had a much lower disease incidence rate than the other groups – 36% lower.
Those who gargled the drug had a slightly lower incidence rate, but it was not statistically significant.
The authors also noted that those who got sick from gargling water had milder symptoms like coughing.
Not so fast…
This study was carried out more than 20 years ago, in 2005, so we had time to poke holes in it. Results from similar studies have failed to replicate these findings and have produced mixed results.
A 2014 study made a similar comparison: gargling with tap water and not gargling at all. They found no difference in who developed an upper respiratory infection.
A meta-analysis of studies from 2005 and 2014 found that there was little to no evidence that gargling with water only contributed to the development of upper respiratory infections.
Another study, done in 2012, found that gargling with water could reduce the risk of young children (ages 2 to 6) developing a fever. The water helped, but the green tea was even better.
Since then, a number of studies have looked at gargling green tea, which contains antioxidants called catechins some researchers say could help us fight colds.
A 2024 study found that green tea helped reduce respiratory infection rates compared to water, while a 2026 study did not find a statistically significant difference between the two.
As for other mouthwashes, a 2025 study found that mouthwashes could be helpful in preventing respiratory illness, although it’s important to note that they only measured symptoms and not confirmed illness.
That said, what we know for sure is that once a person is actually sick, gargling can relieve symptoms, especially with salt water and medicated mouthwash.
According to one study, those who gargled with salt water and rinsed their noses reduced their colds by two days. Gargling with a medicated mouthwash relieved throat pain in another study. Both of these work by reducing swelling.
Gn Health
