The researchers hypothesize that the invading germs trigger the brain to produce the amino acid beta-amyloid as a defence mechanism.

Beta-amyloid is a protein fragment strongly implicated in Alzheimer’s disease. It’s thought to destroy synapses before clumping into plaques that lead to nerve cell death.

The researchers wrote: “Our review proposes the hypothesis that neuroinflammation in [Alzheimer’s disease] might be partially caused by pathogens entering the brain through the olfactory system.”

However, they do qualify that the jury is still out on whether the neuroinflammation comes after developing Alzheimer’s disease or before it.

They noted: “One of the limitations of the ‘infection hypothesis of [Alzheimer’s disease] is the debate of what comes first, the chicken (Alzheimer’s disease) or the egg (infection).

“Is it because subjects have a compromised immune system that they develop an infection leading to neuroinflammation and Alzheimer’s disease?

“Or does increasing inflammation due to ageing and sub-clinical Alzheimer’s disease cause immune defects or unhealthy habits allowing the entry of olfactory pathogens?”

Limitations aside, the study raises the promise of finding new and novel ways of preventing dementia.

The authors of the 2022 study posited that nose-picking damages the nasal mucosa, making it easier for the bacteria to reach the olfactory nerve and enter the brain.

Dementia – how to spot it

Different types of dementia can affect people differently, and everyone will experience symptoms in their own way.

However, there are some common early symptoms that may appear some time before a diagnosis of dementia.

These include:

• Memory loss
• Difficulty concentrating
• Finding it hard to carry out familiar daily tasks, such as getting confused over the correct change when shopping
• Struggling to follow a conversation or find the right word
• Being confused about time and place
• Mood changes