Want to dodge the common cold, flu, RSV, and more? A habit common in Japan could help.
In fact, folks have been doing it multiple times a day for centuries to prevent colds — at school, at home, and at the office. It’s completely free: It’ll only cost you tap water and a few moments out of your day.
Research suggests it might not just be an old wives’ tale or cultural phenomenon.
It’s called “ugai,” rinsing the mouth with water. In Japan, it’s a practice as common as washing your hands. In fact, the gargling’s often done in the same bathroom visit.
The idea is that it’ll dislodge and wash away harmful microbes before they create infection.
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 water significantly beat both the medicine and not gargling when it comes to keeping people healthy. But other researchers say the benefits aren’t so clear cut.
Here’s what to know.
What researchers found
Researchers split 387 participants aged 18 to 65 into three groups: one continuing their normal habits without gargling, one that gargled with water three times a day, and one that gargled with diluted povidone-iodine three times a day.
They continued through the winter cold season, and many became sick over two months.
Those who gargled with plain water had a much lower incidence rate of illness compared to the other groups — 36% lower.
Those who gargled with the medicine did have a slightly lower incidence rate, but it was not statistically significant.
Authors also noted that those who became sick with the water gargle had milder symptoms like coughing.
Not so fast…
That study was done over 20 years ago in 2005, so we’ve had time to poke holes in it. The results of similar studies haven’t been able to replicate these findings, and have produced mixed results.
A 2014 study did a similar comparison: gargling with tap water compared with no gargling at all. They found no difference in who developed an upper respiratory tract infection.
A meta analysis of both the 2005 and 2014 studies found there was little to no evidence that gargling water only helped with developing upper respiratory tract infections.
Another study, done in 2012, found that gargling water could lower the likelihood young children (aged 2 to 6) developed fevers. Water helped, but green tea was even better.
Since then, a number of studies examined gargling with green tea, which contains antioxidants called catechins some researchers suspected might help us fight off colds.
A 2024 study found that green tea helped lower respiratory infection rates compared to water, while a 2026 study didn’t find a statistically significant difference between the two.
As for other rinses, a 2025 study found that mouthwash could be helpful in preventing respiratory illness, though it’s important to note they only measured symptoms, not confirmed illness.
All this said, what we do know for sure is that once someone is actually sick, gargling can help with symptoms — particularly with saltwater and medicated mouthwash.
Those who gargled with saltwater and did nasal rinses shortened their cold by two days, one study found. Gargling medicated mouthwash helped throat pain in another study. These both work by reducing swelling.
