We “Life Extensionists” spend enormous time, thought and treasure trying to optimize our nutritional intake, aka eating – which may happen 4 or 5 times a day. In contrast, every one of the 24,000 breaths we take each day goes straight into our mouth, trachea, bronchi, and lungs – a vast and immunologically suspect gulp of who knows what. Each and every day, our 24,000 breaths bring in 3,000 gallons, 11,000 liters, 388 cubic feet of mostly untreated air. Let’s focus on what may be hitchhiking into our bodies.

It’s winter. Outdoor temperatures have dropped drastically. Inside, you turn up the heat and pull out the space heaters from the back of the closet. You face (and attempt to prevent) the reality of the cold season: Dry, patchy skin, respiratory infections, nose, eye and throat irritation, the flu and miserable colds. We know it is the season for infections, but what’s less apparent are the invisible and infectious monsters that could very well be thriving in our homes.

The culprit: Humidity levels that are perfect breeding grounds for pathogens. Experimental studies on airborne-transmitted viruses, dust mites and infectious bacteria show that the survival and infectivity of these organisms are minimized by exposure to indoor relative humidity ranging from 45-55%.

Here’s a graph that shows what happens outside that optimal range:

We can see the relationship between indoor relative humidity and adverse health effects. For example:

• Dust mites are minimized when relative humidity is maintained below 50%
• Most species of fungi cannot grow unless relative humidity exceeds 60%
• Humidity affects the rate of out-gassing of formaldehyde from indoor building materials, the rate of ozone formation, and the rate of formation of acids and salts from sulfur and nitrogen dioxides.

Careful management of indoor relative humidity is clearly a key factor to maintaining healthy indoor air quality. Just like the need to ensure that e-coli, botulism, insect parts and other junk is kept out of our food supply, you can craft and manage your own perfect pathogenic valley of death, resulting in a healthier, more comfortable home and work environment.

A simple rule: Keep indoor humidity between 45 – 55%, the safe range where air-borne transmitted pathogens, mites and fungus die before they can get (in)to you.

Next up: How to measure and manage indoor relative humidity in the real world.

Ref: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1474709/pdf/envhper00436-0331.pdf

Credit: Indirect health effects of relative humidity in indoor environments.
A V Arundel, E M Sterling, J H Biggin, and T D Sterling
Environ Health Perspect. 1986 March; 65: 351″“361.
PMCID: PMC1474709