Humidifiers: How They Work and How Useful Are They?

Have you ever felt so hot and sticky in your living space even when you're doing nothing? This is usually a sign that humidity is very high. Humidity is the amount of water vapor present in the air. It is affected by the weather and climate in your area. 


Measuring humidity

Relative Humidity (RH) is a unit of measurement that indicates the level of humidity. It is the percentage of the amount of water vapor in the air compared to the maximum amount the air can hold at a given temperature. The higher the temperature, the more moisture the air can hold in total. So basically, the warmer the air, the higher the percentage of relative humidity and when the relative humidity percentage is low, the air feels cooler than the real temperature.

The hygrometer is a device used to test humidity levels. It looks like a thermometer but instead of measuring the temperature, it measures the amount of moisture in the air. 

Humidifiers are equipment that increase humidity by adding more moisture in the air. Conversely, dehumidifiers reduce moisture in the air to lower humidity levels. These devices can use integrated hygrometers or humidistats to manage humidity levels within a desired range.


Effects of Low Humidity

When humidity is low and the air dry, we can experience dry skin, sinus congestion/headache, dry throat, nose irritation, bloody noses, irritated vocal cords, dry cough and cracked lips.

When humidity is also very low, objects catch fire more easily. That is one reason why forest fires happen in places with low humidity. Leaves and wood become very dry, becoming potential fuels in the forest, easy to ignite and start a wildfire. The air has to have a good amount of humidity to release moisture in the air which will eventually become rain. Every time it rains, the potential fuels are prevented from drying up.


Effects of High Humidity

The Philippines has relative humidity varying between 71% in March and 85% in September. For tropical countries with humidity above 60% such as the Philippines, humidifiers can actually be harmful. 

Too much moisture in the air can cause health problems rather than prevent them. It can trigger or worsen asthma and allergy symptoms.

High humidity levels can also lead to condensation on walls, floors and other surfaces, making your home feel stuffy. It also encourages more rapid growth and spread of dust mites, mildew, mold and harmful bacteria throughout the house.

Besides the negative health effects, high humidity can also damage electronics and furniture.


Ideal Humidity at 40% - 60% RH to Prevent the Spread of Virus

People became more interested in humidifiers in mid-2020 due to news about coronaviruses transmission being reduced when humidity is high enough.

A Yale research team, led by Dr. Akiko Iwasaki, found that relative humidity lower than 40% increases the chances of catching the coronavirus. According to them, low humidity impairs the respiratory immune system's defenses. The dry air makes the mucous membranes in our noses dry and more prone to infection.

Low humidity also increases the virus' "float" time. The aerosols a person with respiratory viral or bacterial infection releases through inhaling, coughing, sneezing or talking will absorb less moisture and remain small and light, floating in the air longer. Because of this, more people will likely be exposed to the virus.

Lastly, low humidity extends the virus' survival time. Viruses survive on surfaces and in the air but they also naturally die within hours to days. However, when there’s too low or too high humidity, the virus might continue being active even after drying.

The range of humidity that best reduces transmission is reportedly between 40-60% RH. If relative humidity is below 40%, a humidifier may help you reach the desired humidity range. 


Types of Humidifiers

There are various types of humidifiers and they work in different ways:


  • Central humidifier

A central humidifier is built directly into your home’s heating and air conditioning system. It is designed to humidify the entire house. There’s no need to refill the water supply since it’s also connected to your plumbing systems. However, this type of humidifier is usually not used in the Philippines since our humidity level is high.


  • Ultrasonic humidifier

An ultrasonic humidifier is a quiet device that produces either warm or cool mist with the help of high frequency ultrasonic vibrations that turn water into vapor fast. It creates water droplets that lift into the air as a fog. However, if there are pathogens in the water, it will spread in the air along with the water. This may create dust and cause irritating allergies.


  • Impeller humidifier

Impeller humidifiers use a rotating disk that spins at a high speed to produce a cool mist rather than using heat to convert it into steam. This device is a good choice if you have children as it carries no risk of burns. Impeller humidifiers are more affordable compared to other types of humidifiers but it only works for single rooms. It can also bring difficulties for people with allergies and asthma if the water in the humidifier is not regularly changed since the water will stagnate and release bacteria with the fog.


  • Evaporative Humidifier

Evaporative humidifiers rely on evaporation instead of using heat or vaporization. They use a simple fan to blow air through an absorbent material like wet wick, filter or belt. These humidifiers can self-manage how much moisture they put into your house so when humidity starts to reach a certain level, less moisture will evaporate out into the air to keep things at an equilibrium. It only works in one room at a time since it humidifies the water more slowly than ultrasonic humidifiers.


  • Steam Humidifier

As its name suggests, a steam humidifier creates steam in the room by electrically boiling water and then cooling it down before expelling it into the air. Some people add medicated inhalants or essential oils when using this humidifier. However, aroma oils/inhalants can be considered allergens or pollutants harmful to health. This type of humidifier is not suitable to houses with children as it may cause burns if spilled.


Maintaining Your Humidifier

If you use a humidifier, make sure it is regularly cleaned and well-maintained. Bacteria and mold can grow in a dirty humidifier and you can breathe them in if they get sent out into the air.



Humidifiers are useful when relative humidity is low, typically below 40% RH. However, the ideal humidity level ranges between 40-60% only. Using a humidifier here in the Philippines when humidity is typically above 60% RH is usually not a good investment. In fact, dehumidifiers that reduce moisture from the air to lower humidity may be more useful here.

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