1. Lack of fresh oxygen, no natural air

This is due to living in an air conditioned environment most of the day(and night). It deprives us of the natural temperature flux our bodies expect. Plus it circulates and recycles stale air lacking in beneficial negative ions found in abundance outdoors.

Even those who go for a jog or walk in the morning end up clogging their lungs with polluted air.

Metro air pollution from cars, industry, and high population density can irritate lungs and accumulate over decades as there is nowhere for the air to escape and there aren’t enough trees to filter the air.