I used to think gargling salt water was something grandmothers recommended because grandmothers recommend everything. Then a Japanese study from Kyoto University — a randomized controlled trial with nearly four hundred people — found that gargling plain warm water three times a day reduced upper respiratory infections by about forty percent. Plain water. Not salt water. Not mouthwash. Just warm tap water.

I started doing it. I have not had a proper cold in two winters. Maybe coincidence. Maybe the study was right.

The science (what we know)

The throat is a major entry point for cold viruses. Gargling creates turbulence that physically dislodges viral particles from the throat lining before they can establish an infection. Warm water also increases blood flow to the mucous membranes, which may boost local immune response.

The Kyoto study specifically tested water at about 104°F (40°C) — warm enough to be comfortable but not hot enough to burn. Participants gargled three times a day for fifteen seconds each time. The control group did nothing. The gargling group had thirty-six percent fewer colds. A 2020 follow-up study confirmed similar results with a larger sample.

How to do it

1. Run the tap until the water is warm — not hot, just comfortably warm. Think bathwater temperature.
2. Take a mouthful and tilt your head back.
3. Gargle for fifteen seconds. Use a timer the first few times — fifteen seconds feels longer than you think when you are gargling.
4. Spit. Repeat two more times during the day — morning, after work or school, and before bed.

That is the whole routine. It takes about a minute total across the entire day.

Does salt water work better

Salt water gargling has its own evidence base — it can soothe an existing sore throat and may reduce the severity of symptoms. But for prevention, the Kyoto study found plain warm water was just as effective. Salt is not necessary unless you are already sick. Plain water is easier, cheaper, and you cannot accidentally use too much salt and irritate your throat.

When this is especially worth doing

• Cold and flu season: October through March. Start gargling when people around you start coughing.
• After being in crowded places: Airplanes, public transit, concerts, schools. Anywhere you have been breathing shared air.
• When someone in your household is sick: You are exposed anyway — might as well flush the virus before it takes hold.

I keep a small cup in my bathroom now. I gargle while brushing my teeth. It is such a minor habit that I forget I am doing it most days. Two winters without a cold is not proof — but it is enough for me to keep going.