A study out of Griffith University headed by Professor James St John suggests that picking your nose may increase the risk for Alzheimer's and dementia.

Chlamydia pneumoniae (not the sexually transmitted Chlamydia) has long been suspected to be a factor in Alzheimer's and dementia, but the pathway past the brain-blood barrier had yet to be discovered

The Griffith study showed that the bacteria can use the nerve extending between the nasal cavity and the brain as an invasion path to the central nervous system. The brain responded by depositing amyloid beta protein, which is a hallmark of Alzheimer's disease.

At least that's what happens in mice.

St John's next step in research is to prove that human brains can be accessed by the bacteria via the same olfactory nerve. He says,

We need to do this study in humans and confirm whether the same pathway operates in the same way. It's 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.

In the meantime, he suggests that everyone stop picking their nose and plucking their nose hairs just to be on the safe side.

"We don't want to damage the inside of our nose and picking and plucking can do that. If you damage the lining of the nose, you can increase how many bacteria can go up into your brain."

Maybe that explains some things.