Does UV light Kill Mold and Mildew?

Nothing is more frustrating than dealing with mold on a hot and humid day. While there are plenty of ways to prevent fungi growth, UV light is a viable option to kill mold and mildew that many people have forgotten. In this guide, we will look into how ultraviolet light works, the different types of germicidal UV light, and its effectiveness against mold. At the end of the post, we will recommend the best UV air purifier you should buy. Let's begin.


Mold is a never-ending problem for folks that stay in a hot and humid area. People have been all kinds of ways to prevent pathogens from infesting their homes to no avail. On a bad day, mold remediation can cost $7500, especially when extensive damage occurs. A more significant concern than the financial burden is the health complications mold brings. You are at risk of allergy symptoms such as cough, skin irritation, headache, lung infection, and other respiratory diseases. It can also exacerbate asthma or other breathing problems when not dealt with. To prevent all that from happening, we will focus on the brighter side; of how ultraviolet light can be the perfect tool to destroy mold and mildew.

Can Ultraviolet Light Kill Mold And Mildew?

Similar to the power of sunlight, ultraviolet radiation kills biological pollutants like mold, powdery mildew, fungus, germs, bacteria, and viruses in the air and surface area. A scientific study by Duke University Medical Center and the University of North Carolina Health Care shows UV light can reduce more than 91% of pathogens in a hospital. Ultraviolet light composes a discrete portion of particles or quantum electromagnetic radiation called photons. With a wavelength from 10 nm to 400 nm, photons will transmit a high-level electromagnetic energy that vibrates to create a trace of light wavelength. The shorter the band, the higher vibration, and frequency of the UV light; the more energy is produced.

Mold spores and other microorganisms are vulnerable to the germicidal effects of a properly designed UV lamp. A proven technology that has existed since the 18th century. UV light is widely used in meat processing, industrial processes, underground basement, healthcare centers, and hospitals e.g. surgical room. You can also find UV light used for microbial sterilization in water treatment, medical equipment, air purification, and food sanitization.

Besides killing and preventing mold growth, the right doses of UV rays can improve mood and boost energy levels. Ultraviolet light is also used in skin therapy by stimulating the body to produce vitamin D. Vitamin D can help treat skin disorders and regulate calcium metabolism, insulin secretion, and blood pressure.

The benefit of ultraviolet light is it kills mold and other fungi without releasing chemical byproducts. According to U.S. Environmental Protection Agency (EPA), UV light is recommended over biocide, chlorine bleach, ammonia, and other cleaning agents that off-gasses harmful toxins with adverse health effects. Compared with UV, chemicals adhere to a surface area for much longer and can cause sickness when inhaled. In the long run, it can also damage household materials like plastic.

Can Ultraviolet Light Kill Mold And Mildew

How Does UV-light Kill Mold And Mildew?

Through proper exposure, UV-C light short wavelengths of 100-280 nanometers (nm) irradiate high-level electromagnetic energy to effectively kill mold, mildew, bacteria, and viruses by penetrating the nuclei acid cells and inducing damage to the microorganisms’ DNA. By changing the arrangement of the molecules, defective cells will be inactivated, therefore, lose the ability to reproduce, spread, and trigger an allergic reaction.

How Long Does UV Light Take To Kill Mold?

In general, UV-C light takes 1 to 2 hours to kill 99.9% of the mold. However, the exposure time will vary depending on the UV light intensity and the proximity of the mold. You will also need to factor in the UV-C Light exposure time, the cooling effect of airflow, the strain of the mold in resisting UV irradiation, the lightbulb types (UV-A, UV-B, UV-C), room size, and the coated material of the light bulb (phosphor, quartz, LED). The longer the mold dwells inside the UV chamber, the more fungus will be destroyed.

There are 3 types of ultraviolet wavelengths you cannot differentiate by the human eye. UV-A (longest wavelength) is known as the backlight, an invincible light primarily in tanning beds. UV-B (medium wavelength) is invisible rays that come from the sun. UV-C (shortest wavelength) or germicidal UV is the most common type found in most medical equipment, HVAC systems, and home appliances due to its strong disinfectant element.

Note that UV air purifiers and UVGI have limitations in killing mold spores and fungus. According to the U.S. Environmental Protection Agency (EPA), a standalone UV-C air purifier is less effective than a multi-stage filtration system. A multi-stage filtration with HEPA and carbon filters can trap dormant pathogens, including dead mold spores that still produce and trigger allergic reactions. There is also ozone emission and mercury risk if the UV lamp is not handled correctly. It can lead to sunburn, mercury poisoning, and eye damage upon exposure.

To ensure the ultraviolet light runs at maximum efficiency, turn off all light sources in the room, including doors and windows. Replace the light bulb prior to depletion, as the UV radiation effectiveness will gradually decrease upon use. The weaker the light intensity, the longer UV exposure it takes to destroy the mold and microbes. Regular cleaning is needed to keep the UV light bulb dust-free. A dirty UV bulb or chamber will reduce the sterilization performance as the dust blocks the ultraviolet light from irradiating. Lastly, place the UVGI air cleaners near a mold-infested area, like a moist and shaded basement with no sunlight. If the UV light fails to hit the mold, the germicidal effects will have zero impact.

UV light air purifier kill mold

Is Ultraviolet Light Safe For Humans?

While harmful to microorganisms, short-wavelength UV-C light is safe for humans because it has a limited range (100–280 nm) that cannot penetrate through the outer cell of human skin or the tear layer in the eye. Most UV lamps come with a coated lamp or ozone block that further reduces ozone emissions. That said, you should never look directly at the UV lamp while operating.

Like an ionizer, the UV light will emit ozone byproducts but at an insignificant concentration level (<0.050 parts ppm concentration adopted by California Air Resources Board). Oxygen will break into two atoms and merge with other oxygen molecules to transform ozone (O3) through photolysis. Depending on how susceptible a person is to ozone, it can exacerbate cough, chest pain, sore throat, inflammation, and shortness of breath. Long-term exposure can scar lung tissues and damage the skin cell resulting in premature wrinkles, sunburn, acute photokeratitis, and skin cancer.

The Alternate Ways Of Dealing With Mold

Dead mold spores can still cause allergic reactions and trigger an asthma attack. Use natural ingredients like vinegar, baking soda, or hydrogen peroxide to clean and scrub off surface mold and mildew. Keeping room humidity between 30 to 50 percent is the best solution to prevent mold and mildew growth. Under a low humidity environment, use a humidifier to add moisture back to the room. Conversely, use a dehumidifier to remove moisture from the room. Perhaps the most critical of all, close all windows and fix any leakage that allows external moisture from getting in.

Final Thoughts

Whether as part of water or air cleaning appliances, UV light should be part of your sterilization tool, and it is universally proven effective in containing mold. Here are more tips to get start your mold-free journey:

  • Inspect and assess the mold damage in your home.
  • Look for mold infestation in common areas like the basement, bathroom, air ducts, cooling coils, drain pans, pipes, underneath the sink, and other humid areas. If there's a heavy scent of mustiness, there could be mold growing in porous materials like ceilings, walls, and wooden tiles that you cannot see.
  • Install a UV lamp as part of the HVAC systems or get a powerful UV air purifier with a HEPA filter that passes CARB and FDA stringent standards. Check the boxes for ARB Certified label or visit their website to verify the product's authenticity.
  • Consider mold remediation only as a last resort. It is costly and time-consuming.
  • Always leave your UV light air purifier on during mold remediation to give you additional protection against mold spores reintroduced back into the air.

Max Fernandez

A loving father and a dedicated reviewer for airfuji.com with more than 1000 air purifiers under his belt. Max Fernandez is also one of the million patients currently suffering from asthma. Feel free to nudge him if you have any questions.
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