Answer:
Our bodies deliberately send more blood to an erectile tissue between the two nostrils to increase its size and direct the air flowing through one of the nostrils. After a few hours, the airflow switches to the other nostril.
Explanation:
I’ll bet most people don’t realize that when you breathe through your nose, you do so more from one nostril than the other and your body knows to switch to the other nostril every few hours. I had no idea. I’m only aware of any difference in my nostrils when I’m congested!
This nasal cycle is controlled by the autonomic nervous system which also controls things we don’t think about like heart rate and breathing
Why do we do this? Some scientists believe the alternating airflow allows each nostril to maintain optimal moisture levels so no one side gets dried out. It may also protect against respiratory infections or allergies.
Others believe it’s tied to our olfaction or sense of smell. It’s possible that the quicker and slower airflow in each nostril optimizes us to the vast range of smells. Some smells take longer to detect and transmit to the brain.
The liver makes sure that blood glucose levels remain steady. But when blood glucose levels fall, the pancreas secretes glucagon. Therefore the answer to your question in the pancreas.
It's due to the increased production of Melanin that helps block UV light
