Picking your nose and plucking the hairs from your nose are not good ideas, particularly if you don’t want to get Alzheimer’s disease.

A growing body of evidence shows that damaging the lining of your nose gives bacteria and viruses a clear pathway to the brain, where they create some of the pathologies of Alzheimer’s disease. And picking and plucking your nose are two easy ways to damage that lining.

Three in ten people will develop Alzheimer’s disease and dementia, and there are several risk factors, including genetics and age, the number one predictor. Once you reach 65 years of age, your risk factor increases, but scientists are looking at other causes as well, because it’s not just age—it is environmental exposure as well. And we think that bacteria and viruses are critical.

If you inhale oxygen, you’re taking in bacteria and viruses, and these microbes can affect your sense of smell. We don’t think that’s a coincidence. Our research shows that one pathogen, chlamydia pneumonia, can travel up the nose and straight into the brain where it can start off pathologies that look like Alzheimer’s disease. Researchers at the Clem Jones Centre for Neurobiology and Stem Cell Research saw this happen in a mouse model, and the evidence is scary for humans as well.

It’s likely that chlamydia pneumoniae is not the only microbe that can take this pathway to the brain. There are a whole range of different pathogens that can impact your sense of smell and potentially contribute to the development of Alzheimer’s disease.

“Three in ten people will develop Alzheimer’s disease and dementia.”

How our study worked and what it said about how pathogens get to your brain

Researchers infected the nose of mice and then looked for whether bacteria had travelled up into the brain. We found that very quickly, within days, the bacteria were in the brain setting off a cascade of effects including gene changes and protein changes like what we see in humans and which are tell-tale signs for the onset of Alzheimer’s and dementia.

We’re the first to show that this microbe can go directly up this pathway: up through the nose and into the brain. What’s next is that we need to do this study in humans and confirm whether the same pathway operates in the same way. Its research that has been proposed by many people, but not yet completed. What we do know is that these same bacteria are present in humans, but we haven’t worked out how they get there.

Why the nose?

Once the bacteria get into the olfactory nerve, which is directly exposed to the air (it’s how we smell odours), it’s like a direct highway between the outside world and your brain. It’s a short distance and the route also bypasses the blood-brain barrier, which is one of the brain’s best protections against infection by bacteria and viruses.

We’ve also shown that bacteria and viruses can go up through the trigeminal nerve in a similar way. This is a nerve that provides sensory and motor innervation of the face and then goes into the brainstem. That means that two regions of the brain where some of the first symptoms of Alzheimer’s and dementia show up in humans, the olfactory region and the brainstem, are the locations where these two nerves go into the brain.

We don’t think it’s a one-off bacterial infection that causes these pathologies. It can happen slowly over your life. These bacteria are living inside the cells of the nose and olfactory nerve. And we think they might stay there for years, living inside our brains and doing small amounts of damage over time, and that might be what contributes to Alzheimer’s disease.

The damage happens in small increments, so we can think now about how we can reduce infections or how to treat them early on and reduce the long-term risk of degenerative disease. It’s our great hope that we can now reduce the progression or symptoms of Alzheimer’s disease using this knowledge.

One of the symptoms of Alzheimer’s disease is the presence of beta amyloid peptides or amyloid peptides. People with Alzheimer’s disease often have more accumulation of these amyloid peptides in plaques. This is a protein. This peptide is a protein that’s normally at low levels in the brain but when we infect it with bacteria, we see a large accumulation of this amyloid peptide protein around where the bacteria are.

And so we’re thinking now that these bacteria can set off this secretion of these proteins that lead to these plaques in humans. And now another aspect of it is that if we all have bacteria in our noses, in our brains, and I’m sure we all do, why do some people get it and other people don’t? it might be just because of your genetics or it might be something else, some other environmental factor at the same time.

There are now a lot of people who are looking at how pathogens, viruses and bacteria can cause many diseases in our brain and a lot of fingers are being pointed at bacteria contributing to Alzheimer’s disease. So it’s certainly a great area for developing drug treatments, and our team at the Clem Jones Centre for Neurobiology and Stem Cell Research is already looking at new ways to test for, prevent and treat for Alzheimer’s and dementia.

For example, because the one of the first symptoms of Alzheimer’s is losing your sense of smell, we could screen people using their sense of smell. So perhaps we should be thinking about getting people to do a simple smell test when they get to the age of 60 and use that knowledge to create therapies and potentially treat people earlier.

What the future holds?

We’re looking at moving to human research soon. We want to look at how bacteria can contribute to Alzheimer’s disease in humans, and we’re going to need volunteers to help us do it. We’re in the process of getting ethics approval to conduct that research with human volunteers. This is intensive research that requires many hours of human work. Moving onto research on humans is going to be bigger and more intensive than our work on mice, in many ways, so it will be a huge undertaking.

But even with only our current knowledge, the evidence tells us that we don’t want to damage the inside of our noses, because if you damage the lining of the nose, you can increase how many bacteria can go up into your brain. So, when your mum told you not to pick your nose as a child, she may have also been coincidentally reducing your risk of Alzheimers and dementia later in life—if you listened to her, that is!


Professor James St JohnProfessor James St John is Head of the Clem Jones Centre for Neurobiology and Stem Cell Research. James is a Life Technologist specialising in the creation and translation of therapies to repair injuries and diseases of the nervous system. He has a particular interest in understanding the biology of the olfactory system (sense of smell) and the role of glial cells in the functioning and repair of the nervous system. 

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