The Blood Brain Barrier protects the brain from some things by the BBB.
The brush of the CPR test has little protrusions that hold whatever the manufacturer puts on it, and as the nurse shoves it deep into the nose, it brushes the cribiform plate, and contaminates can easily enter the BBB from this bone.
The cribriform plate is a part of the ethmoid bone in the human skull, forming the roof of the nasal cavities and supporting the olfactory bulb.
It is characterized by numerous small holes, or foramina, which allow the passage of olfactory nerves from the nasal cavity to the brain, enabling the sense of smell.
This sieve-like structure is particularly vulnerable to fractures, which can lead to olfactory dysfunction, cerebrospinal fluid leakage, and potentially meningitis.