Unfortunately, most furnace filters are slid in place without an airtight seal, which allows air to pass around the filters. This problem is worse for the higher-efficiency MERV filters because of the increase in air resistance.
Common Cause is a network of people working to help rebalance cultural values to create a more equitable, sustainable and democratic society. 1  We are all shaped by our culture.
The cause is often not clear. It may be due to a virus, but it can also arise from bacterial infection, head injury, extreme stress, an allergy, or as a reaction to medication. 30% of affected people had a common cold prior to developing the disease.