Does UV Light Kill Mold?

No one wants mold growing on their property, it’s unsightly, it can damage the surface it’s growing on and most of all, it can be harmful to both humans and animals.

So, you may have heard that UV light can kill mold, but is this true? And if so, how and why does it kill fungi, and what is the most effective way that you can use it to eradicate this fungus?

In this article, we will cover all these questions and more, so, for all you need to know about how to kill mold using UV light, keep reading.

Does UV light kill mould

What is mold?

Mold is a structure of fungus, it reproduces and spreads by releasing spores, when these spores find a suitable environment, they create a new colony.

There are thousands of types of mold, but they all have aspects in common, such as requiring water, nutrients, and oxygen to survive. As a result of this, they can often be found growing in damp areas of the home, usually where there is little sunlight (such as basements and attics).

Some strains of mold and mildew are completely harmless to humans, however, many can produce mycotoxins as a defense mechanism whenever they feel threatened. These mycotoxins can be harmful to humans, causing lung and gastrointestinal issues in healthy individuals, and potentially life-threatening complications in those with allergies or weakened immune systems.

What is UV light?

Uv (ultraviolet) electromagnetic radiation is emitted by the sun and from artificial sources such as UV lamps.

It is transmitted in waves that make up the electromagnetic spectrum (EM), which includes microwaves, radio waves, infrared (IR) visible light, x-rays, and gamma rays.

How can UV light kill mold?

UV light is powerful enough to break chemical bonds, and the photons within the rays can cause ionization, which is a process whereby electrons are torn away from atoms. This damages the mold’s DNA, killing it and making it completely sterile.

Breaking down mold at a molecular level makes UV light exposure one of the most effective methods of killing it. It is for this reason, that it is commonly used as a method of killing not only mold, but also bacteria on food items in a process known as UVGI, or Ultra Violet Germicidal Irradiation.

Does a UV light kill black mold?

Yes, whilst black mold (Stachybotrys chartarum), might be one of the more stubborn and tricky to remove molds, UV light will be just as effective at killing it.

The cell walls will become damaged and will eventually kill the mold when exposed to UV light, this is why black mold is most commonly found growing in damp and dark areas of properties where it can grow with as little exposure to sunlight as possible.

Does fluorescent light kill mold?

No, in most cases fluorescent lights and lamps will not kill mold. Although it is true that they do emit some UV light, the levels are very low and will more often than not, be unable to break down the cell walls of mold and bacteria in the same way that specific UV lamps can.

What type of UV light kills mold?

As discussed, UV light will kill mold, however, there are several different wavelengths that it can come in, so let’s now explore which of these wavelengths is most effective at killing both molds, fungi, and bacteria.


Longwave UV light (UVA), which is also known as UVA, is the second most common form of ultraviolet light. This is the type of light that causes items to appear to glow and the type used in sun beds.


Midrange UV light (UVB) is more powerful than its long-range variant and can cause burns to the skin of humans and animals. At this wavelength, some of the sun’s UV rays are absorbed by the ozone layer.


Shortwave ultraviolet radiation (UVC), is the most powerful of all UV rays. However, the atmosphere filters it so that it cannot reach the Earth’s surface.

This type of radiation is incredibly powerful and highly damaging to cells and organic matter, it is for this reason that UVC rays are used to effectively kill mold and its spores.

How to kill mold with UV light

As we have seen, Longwave UVC radiation is powerful enough to kill mold by destroying its DNA, however, not only do the circumstances for remediation need to be correct to be effective, but important safety advice must be adhered to in order to prevent injury or even blindness.

With that being said, use the following steps to effectively kill mold with UVC radiation.

Step 1. Purchase a UVC ultraviolet lamp

Step 2. Identify the source of mold in the property.

Step 3. Wear UVC protective eyewear at all times whilst working with the lamp.

Step 4. Place the lamp directly in front of the mold patch, roughly two to three inches away.

Step 5. Leave the lamp on the mold for at least two hours with no other sources of light in the room.

How effective is UV at killing mold?

Using Ultraviolet radiation is one of the most effective methods of killing mold, as it breaks down its very DNA, making it sterile.

The UV rays penetrate deep into the fungi cells and damage the nucleic acids, after this has occurred, the mold will die within one to two hours.

Having other sources of light in the room you are treating, or having the lamp too far away from the patch you are trying to remove will affect its efficacy, so make sure all other lights are off and the lamp is no further than 3 inches away from the fungi you are trying to kill.

This method is far more thorough than washing away mold with detergent or trying to kill it with bleach, as some strains can withstand harsh chemicals, and spores are easily missed. With UV light, all mold and its spores will be killed.

Can you use UV light to kill mold in a basement?

Absolutely, using UV radiation to kill the mold you have discovered in a basement is an excellent way to remove it.

The fungi will be dead in a short matter of time after UVC exposure, but remember, if the circumstances within the basement don’t change, mildew may return.

Combine using the light to kill the mold, with properly cleaning and drying the basement in order to prevent this.

What are the main advantages of using UV to kill mold?

There are many advantages of using UVC radiation to kill mold over other remediation options, these include:

  • Kills mold completely
  • Kills spores in the air
  • Relatively cheap
  • Simple to use
  • No use of strong chemicals
  • Safe as long as safety precautions are used
  • Can be easily repeated if mold returns

What are the disadvantages?

Of course, like most things, there can be drawbacks to using UVC radiation for mold remediation. Some of these include:

  • Can take up to two hours to be effective
  • Potential for injury if proper safety procedures are not followed
  • Light will need to be applied directly to each patch of mold discovered
  • Can be ineffective if the lamp is too far away or too weak

Which UV lights are best for killing mold?

The power of the UVC lamp that you use will play a large part in how effectively it can kill mold, mildew, and bacteria in your home.

Should you buy a lamp that is not sufficiently powerful, you could well be wasting your time and money. Whilst you are shopping for your UVC lamp, there are two main factors other than the price that you should be looking for.

Firstly, the lamp should provide a wavelength of between 255 to 280 nm, this will be sufficient to kill the fungi in the two-hour period suggested.

Second, is that the lamp should be able to provide a minimum of 8 watts. Weaker lamps will take considerably longer to be effective, and in some cases, may not be effective at all.


How long does it take UV light to kill mold?

Within 2 hours of UVC light exposure with a wavelength between 255 to 280 nm, mold, and its spores will begin to die. Lamps lower than 8 watts may take longer than this.

How much UV light does it take to kill mold?

In order to be effective, UVC light needs to be placed directly in front of the mold in order to kill it. Even in smaller rooms, all other lights should be turned off and any other sources of light should be removed to increase its efficacy.

Does UV light kill mold in a shower?

Yes, UV light is effective in any room of the house, even those highly prone to mold growth. Remember though, if the conditions in a shower or the bathroom it is in remain the same, more mold and mildew are highly likely to return.

Is UV light dangerous to humans?

Yes, UV light in any of the wavelengths (short, medium, or long-range) can be harmful to humans. It can cause serious burns to the skin, blindness, and potentially cancer. It is for these reasons that safety goggles should be used when treating mold with it, as well as taking additional safety precautions.

Does UV light kill bacteria as well as mold?

Yes, UV breaks down cells at their DNA, so it is just as effective at killing bacteria as it is in mold. UV radiation lamps are used in many hospitals to keep bacteria levels low, as well as being used to sterilize water.


UVC radiation is highly effective at killing mold and its spores, as well as other fungi, bacteria, and viruses. Using a lamp that provides a minimum of 8 watts and wavelengths between 250-280 nm will be effective when the lamp is placed 2-3 inches away from the mold patch and left for two hours.

Chris Walker

Chris Walker has struggled for several years with mold after buying his own property. After finding the solutions to several issues around his home, he decided to create this site in order to answer as many questions about mold and mildew as possible to help others dealing with the same problems.

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