Researcher's at Griffith University in Australia think that picking your nose might allow bacteria to enter your nasal passages and have a pathway directly to the brain.
Basically the bacteria can sidestep the olfactory nerve - which is how we smell - and also avoid the bloodstream for that direct path. The researchers have seen the same plaques on the brain that are seen with Alzheimer's. Eventually those plaques cause changes to the neurons in the brain.
Obviously, a lot more research is needed for this. For now, you should probably pick your nose less and also not pluck nose hairs.
Find out more about the study here.
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