On average, the typical American contracts two to three colds per year between September and May, at an estimated cost of around $40 billion to the economy. Effective forms of treating or preventing colds have proven hard to come by, with the majority of over-the-counter medicines yielding modest results; it’s hard to devise a drug that tackles the vast array of viral pathogens that cause them. The need for better respiratory protection during the winter months is clear. It might be found in a practice that dates back thousands of years.

The concept of saline nasal irrigation, or bathing the nasal passages with a saltwater solution, is thought to have been introduced as part of Ayurveda, an alternative medicine system that originated in the Indian subcontinent more than 5,000 years ago. Now, modern science is beginning to demonstrate that this ancient practice really does serve as a surprisingly effective shield against many of the seasonal bugs behind the common cold.

In 2024, a major new study of nearly 14,000 people funded by the National Institute for Health and Care Research in the UK found that using a simple saline-based nasal spray between three and six times a day at the first sign of an infection reduced illness duration by around 20 percent. A follow-up study, published last year, reported similar benefits.

According to Paul Little, a professor in primary care research at the University of Southampton who led both studies, sodium chloride—the chemical name for salt—is capable of stimulating a natural antiviral mechanism within the nose. “The chloride in saline is taken up by the cells of the nose and throat, and converted into hypochlorous acid within these cells which inhibits viral replication,” says Little. “In doing so, the viral load in the nose is reduced.”

Archived medical journals reveal that this practice has been examined as part of Western medicine since the 19^th century, but has often been treated with a degree of skepticism. During the early stages of the Covid pandemic, many health care professionals dismissed the suggestion that saline nasal irrigation might be able to prevent infections. The technique was initially listed among other debunked therapies on the World Health Organization’s Covid myth buster page, before being later removed as a steady trickle of research began to prove that regular use of saline sprays or irrigation really could limit the effects.

One study found that people who practiced saline nasal irrigation for two weeks after testing positive for Covid were more than eight times less likely to be hospitalized, leading to a resurgence of interest among doctors regarding its ability to dampen the effects of other seasonal infections.

“Clinicians and researchers have started paying increasing attention to saline nasal irrigation because it helps, and it is natural, easy to understand care,” says David Rábago, a physician and professor at Pennsylvania State University College of Medicine. “So far the results of many small studies and a few big ones are that saline nasal irrigation is safe and effective.”

As well as blocking viral replication within nasal cells, it appears that saline can increase the activity of a group of white blood cells called neutrophils—which help to fight off pathogens—while also enhancing the ability of mucus to encircle and trap viruses.

“When perfectly hydrated, the mucus cells make a barrier and envelop a virus, so that you can either swallow it where the [stomach] acid degrades it, or cough it up,” says Amy Baxter, a pediatrician and assistant clinical professor in medicine at Augusta University. “It’s kind of like how soap works; it surrounds the dirt and makes it easier for it to come off because it fully envelopes these little particles.”