Your nose knows how to get into your brain.

In Blood brain barrier, Brain Science, Senses and Perception by Brainy Days Ahead

Strep A infections may lead to autoimmune neuropsychiatric disorders in children. Researchers discover that immune cells reach the brain by traveling along odor-sensing neurons that emerge from the nasal cavity, not by breaching the blood-brain barrier directly. The findings could lead to improved methods for diagnosing, monitoring, and treating these disorders.