How Does Relative Humidity Affect Your Health?

Dehumidifiers are crucial for maintaining the humidity level in your home, but how much does humidity matter? Humidity can actually play a large role in the health of you and your family. In fact, extreme humidity, whether high or low, can increase the spreading of airborne sickness, allergies, and chemicals. You see, all of these factors have an ideal relative humidity level that will minimize growth. In the majority of cases, 40-60% relative humidity is the range you want to maintain in your home. When the humidity levels rise too far above 60%, not only will you experience discomfort but, you and your family are much more likely to experience unfavorable conditions.

Airborne Sickness

One of the harmful effects of high humidity is the spreading of airborne sickness through increased bacteria. So, how exactly does humidity affect the growth of bacteria in your home? Well, the relative humidity level can actually alter the survival rate of bacteria by affecting the strength of the cell walls. Bacteria cells are weakened the most during the 40-60% humidity range. Numerous studies have shown that outside of this range, it’s more plausible that bacteria will survive and multiply. For instance, it’s been shown that E.coli is less likely to survive in the mid-humidity range. Another example would be mycoplasma pneumonia, which studies have shown will survive longer in high or low humidity levels.

Similar to bacteria, extreme relative humidity levels are more conducive to the survival of viruses. Depending on the exact molecular structure, viruses typically prefer either extremely high or extremely low humidity levels versus a moderate humidity level. Viruses that prefer humidity under 50% include rubella and measles. On the other hand, many viruses, such has adenovirus and coxsackie, have a molecular structure that thrives in humidity levels above 70%. Certain viruses can survive well in both high and low humidity environments. One experiment showed that influenza survival was highest when the humidity was very low (20% RH) or very high (80% RH) with a decrease during the moderate stages of humidity. Overall, studies have proven that the occurrence of viruses was lowest in homes when there was a 40-60% humidity range.

Humidity will also have an effect on frequency of respiratory infections. Just like bacteria and viruses, respiratory infections are more likely to occur if the environment is high or low in humidity. One study compared the rate of sickness in children in relation to the humidity level in their bedrooms. The results showed that there was a higher incidence of respiratory conditions in children whose bedroom humidity level was above 75%.

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In addition to increasing your likelihood of getting sick, humidity levels also create a higher chance of allergies. The most frequent causes of allergies are dust mites and fungi. Incidentally, the rate of dust mites and fungi increases as the relative humidity level increases.

Dust mites may seem harmless but, they are in fact the most common reason for household allergies. Experiments show that dust mites are most common at 80% relative humidity. While there are other factors that could affect dust mites, such as cleanliness of the home, studies have proven relative humidity to be the single most important factor.

Fungi, another major cause of allergens, excels in high humidity environments. Known to cause reactions such as asthma, or rhinitis, most fungi grows in environments with higher than 75% relative humidity. Consequently, if there are areas in the home with high humidity, such as bathroom walls, a damp crawl space, or even wet ceiling tiles, that is where you find fungi. It can also be found in organic materials that are damp, ranging from carpets to furniture stuffing.

Once fungi starts it will continue to spread throughout your house. A simple way to prevent this from occurring is to maintain the humidity level in your home so you can avoid the extremely high relative humidity levels.

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Another element that could affect your family’s health is the spreading of chemicals. Humidity is quite capable of causing harmful chemical reactions within your home. Many chemicals found in building materials are water-soluble, so as the humidity increases, off-gassing of chemicals is more likely to occur. For instance, field studies have shown that formaldehyde, found in foam insulation and textiles, is more likely to be exposed in high humidity environments. Humidity can also have an effect on sulfur, nitrogen dioxide, and ozone levels.

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Health Effects of Humidity Chart

As the chart illustrates, there is an ideal range for the humidity levels in your home. By maintaining a 40-60% humidity level, you can reduce the likelihood of airborne sickness, allergens, and chemicals infiltrating your home. To stay in the optimum humidity zone, it’s important to not just treat high humidity areas but, maintain your entire home consistently. To do this, it can be helpful to use the assistance of a crawl space dehumidifier, which can effortlessly maintain your desired humidity level in the entire area.

Arundel Et Al., (1986) Indirect Effects of Relative Humidity in Indoor Environments. Environmental Health Perspectives, 65. Retrieved from

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