Why do we get colds?
Colds happen when sufficient cold germs penetrate the protective mucus lining of your nose nostrils. This is especially true when the mucus lining has been compromised and no longer provides protection, as well as when the number of cold germs are high. Even healthy people catch colds if too many cold germs penetrate the damaged mucus lining of your nostrils and respiratory tract.
What causes my mucus linings to be damaged?
Extreme low humidity conditions dry out the protective mucus in your nostrils and respiratory tract, causing inflammation and compromising your nostrils, making you susceptible to a cold virus attack. This is especially true if one has a weakened immune system and/or in crowded rooms where the number of cold germs are high. Cold germs can now easily penetrate the compromised protective mucus lining of the nostrils and respiratory tract. The following is a chart that show the effect of humidity
When am I most susceptible to getting a cold?
Aircraft use about 50% cold air and 50% recycled air for the interior of the cabin. This new cold air keeps the humidity down at about 12%. Normal humidity is about 35 to 60%. You are at risk of catching a cold due to the extreme low humidity, recycled air, and crowded conditions, where there is a possibility of higher concentration of cold germs.
During Cold Winter Days & Nights
Again, cold air contains low amounts of moisture, which occurs often in the winter. Indoors some air is recycled but some new low moisture cold air enters the heating system to keep the building warm. The cold air, outside or brought inside, keeps the humidity down to low levels with many times less than 35%. In these cold winter conditions, you are at risk of catching a cold due to low humidity and inside recycled air. This is why there are far more winter colds than other times of the year.
When in Crowded Rooms or Spaces
There is a chance that there is a significant greater number of cold germs circulating in crowded rooms that increases the possibility you may catch a cold. Especially if the humidity is low in the room like it is many times on flights and in the winter.
When Suffering from a Weakened Immune System
When a person is ill or with poor health habits the immune system can be weakened and subject to more susceptibility to catching a cold.