Nasal rinsing or irrigation is an increasingly popular technique to manage hayfever and other irritants in the nose. It involves pouring or squirting a solution into the nose to help wash out microbes, mucus and other debris such as dust or allergens.

There are specialised containers called neti pots that are used to pour water into one nostril, allowing it to run out of the other by tilting your head to the side. Water bottles and other specialised sprays pre-filled with saline solution can also be used.

But the practice is not without its risks, not least because if not done with sterile water it can introduce germs into the body. A small number of people, especially those with weakened immune systems, have even died from diseases caught through nasal rinsing.

So how can allergy sufferers reap the benefits of nasal rinsing while avoiding the pitfalls?

Rinsing the nasal passages with any liquid – sterile or otherwise – may increase the risk of infection. The nose is home to a host of microbes, which help protect body surfaces. Rinsing may remove or kill these good microbes, providing an opportunity for pathogens to enter the body.

However, the biggest risk comes from germs that might be in the liquid – so any fluid poured into the nose should be sterile. The sterile nasal sprays available widely from pharmacies, for example, are not associated with this risk. But tap water is not sterile.

A recent study identified ten people who had undertaken nasal rinsing in the US and contracted acanthamoeba amebae. While the risk is low for most healthy people, infection with this parasite can be fatal for people with weakened immune systems. Three of the ten people in the study died, but another study found 82 percent of US cases of the infection are fatal.

Another amoeba found widely in our environment is naegleria fowleri, which has a 97 percent fatality rate in detected cases – even for otherwise healthy people. Thankfully cases of infection from this parasite are rare too, but using tap water for nasal rinsing and fresh water swimming have been linked to infection.

It is also likely that infections and deaths are much higher in countries where access to clean water is limited.

The US study may have been small but others have found dangerous assumptions about the use of tap water in medical devices. Research conducted in the US in 2021 found that 50 percent of people thought tap water was fine for nasal rinsing – and cleaning contact lenses (another dangerous mistake).

Why is the nose a danger zone?

Blood vessels are close to the surface in the nose and sinuses making it easier for pathogens to enter the blood stream. The vessels also dilate when inflamed due to allergies bringing them even closer to the surface, increasing infection risk, especially if they rupture.

These blood vessels drain an area known as the "danger triangle of the face" – between the edges of the mouth and the top of the nose, between the eyes. The veins from this region run back into the skull and connect with the vessels that drain the brain, providing a pathway for microbes to travel from the sinuses into the brain where they can cause serious infections and potentially even death.

Such cases typically begin as brain inflammation or rhinosinusitis, as seen in the study, which can progress to a cavernous sinus thrombosis.

This is when any infection, such as sinusitis or a spot on the face, spreads into the cavernous sinus, which drains blood from the brain. As a defence mechanism the body attempts to stop the infection spreading by forming a clot to reduce blood flow from the brain, increasing pressure.

It's not just the nose

The nasal passages include more than just tubes that run down to the back of the throat. The tubes connecting from the ear, known as the eustachian tubes, open into the back of the nose on either side. Also attached to these are a number of sinuses, which are blind-ended spaces that serve a variety of functions.

For example, they reduce the weight of the skull, give a buffer zone for trauma to the face and provide an increased surface area to warm and moisten inhaled air. The nasal passages, then, are much more expansive than it might seem.

Their close proximity to other structures is the reason, for instance, that the forehead, eyes and teeth hurt during a cold. Nasal passages are located near the nerves that supply the teeth and these spaces fill with mucous and become generally inflamed and painful.

This also means that allergens and microbes can work their way into these areas too.

These spaces are lined by a special type of epithelium – the tissue that covers all body surfaces. Epithelium contains cells that produce mucus and have hairs, called cilia, on their surface.

These are two of the body's mechanisms to try and keep germs out of the body. The mucus acts like a glue to catch them so the cilia can move them down the nasal passages to a place where they can be blown free of the body, picked out of the nose, or swallowed.

Who should avoid nasal rinsing?

Those with any kind of sinus or ear infection should avoid nasal irrigation until it has cleared up. Rinsing can increase the pressure in the ear tube or spread pathogens into other areas where they may cause further infection or discomfort.

Those with already dry nasal passages or sinuses may find that irrigation can exacerbate the problem. This is because, as it evaporates, the liquid can remove some of the body's natural protective lubrication.

If nasal rinsing sounds like something that may be helpful, ensure you use sterile saline solution. If you must rinse with tap water, it should be boiled and allowed to cool before use.The Conversation

Adam Taylor, Professor and Director of the Clinical Anatomy Learning Centre, Lancaster University

This article is republished from The Conversation under a Creative Commons license. Read the original article.