At What Humidity Level Does Mold Grow?

At What Humidity Level Does Mold Grow featured photo

Nothing hurts (and literally hurts) the eyes more than the sight of icky, funky, greenish-black mold. In some cases, it may seem like a minor issue. However, it can have serious health implications and do significant damage to your home.

Understanding the humidity levels at which mold grows is key to preventing it from thriving and protecting the health and safety of your family and home.

In this post, we’ll tackle exactly that and provide you with practical tips for keeping mold growth at bay.

What Is Mold?

What is Mold

It’s pesky and can be a pain to get rid of.

A mold is a form of fungus that can grow on practically any organic material and thrives in damp and humid environments. It’s made up of small spores that can form mold colonies when they settle on suitable surfaces in your home with access to moisture.

So, when there is a presence of moisture and oxygen, there’s a chance that molds will grow.

Mold travels on your wooden furniture and wall cavities. Food, ceiling, tiles, insulations, and carpets will also absorb black mold. These nasty fungi can also grow on wet areas in your home like the bathroom and kitchen sink and they can produce mildewy or musty odors.

Potential Dangers of Mold in Your Home

Potential Dangers of Mold in Your Home

Mold is manageable, but if you don’t address the moisture problem right away, it can lead to serious harm and damages.

Mold Can Damage Your Home’s Structure

Mold can weaken and ruin structural materials like wood and drywall. It can cause enough damage to collapse walls, floors, and ceilings if you ignore it. This might result in expensive repairs or possibly leave your home unsafe for you to live in.

In addition to structural damage, mold can also cause damage to your personal belongings such as furniture, clothing, and other home items.

You may not see the degree of the damage immediately, but it will slowly (but surely) get to that point.

Mold Can Affect Your Family’s Health

Small amounts of mold rarely cause serious health problems. However, it can pose potential health risks if you don’t take care of it at the onset.

Mold can cause a variety of health problems including allergic reactions, coughing, sneezing, and trouble breathing. It can also result in skin rash and irritate your eyes, nose, throat, and lungs, causing them to become itchy, dry, and inflamed. Many people find that a dehumidifier helps reduce coughing if they are dealing with a high humidity mold allergy situation.

People who have compromised immune systems may be at a higher risk. It can sometimes lead to more significant health issues such as infections.

Mold and Humidity

High humidity levels in the air, in particular, provide the ideal environment for mold growth. When the relative humidity (RH) in an environment is too high, the air cannot hold all the moisture it carries. So, the excess moisture condenses on surfaces. And this provides the perfect breeding ground for mold.

In addition, high humidity levels can make it harder for the materials to dry out after being wet, providing an excellent breeding ground for mold spores.

Causes of High Indoor Humidity Levels

While we already know that too much moisture can result in high humidity levels, certain factors like climate and weather are simply beyond our control. So, when the humidity outside gets high, you can expect the humidity levels indoors to also go up.

That said, it’s important to understand what causes high humidity levels in your home. Here are some of the most common:

Temperature change

Temperature and humidity are related. Black mold thrives in warm environments. However, it may also survive in temperature ranges where warm air meets cool air. In certain places, water vapor can condense which increases humidity.

Many fungi survive at temperatures ranging from 60 to 80 degrees Fahrenheit. And unfortunately, that range is also the perfect temperature for us humans.

Lack of ventilation

Without adequate ventilation, the air inside your home becomes stagnant and humid. This is especially common in homes with inadequate insulation or tight construction.

Old HVAC systems

Your heating and air conditioning systems contain evaporator coils that extract humidity from the air as they run. So if your HVAC system isn’t running optimally, you may expect high indoor humidity levels.

Certain appliances like dryers and humidifiers can also add moisture to the air.


Whether in leaky roofs, windows, or plumbing, it can cause higher relative humidity in your home.

Cooking and bathing

Ordinary everyday chores like cooking and showering might result in high humidity levels in your home. Both can produce steam and moisture. These two provide the perfect breeding ground for mold growth.


We all love some greenery in our homes, but they’re not the friendliest guests when it comes to keeping the ideal humidity level to prevent mold. Plants release moisture into the air through a process known as transpiration. And this can result in high humidity levels.

At What Humidity Level Does Mold Grow?

At What Humidity Level Does Mold Grow

Mold and mildew growth is most likely in environments with a relative humidity greater than 60 percent. However, that mold can develop at lower humidity levels as well. This is especially true when the source has enough moisture in it.

If there’s a leak or spill in a low-humidity room, for example, mold may be able to grow if you don’t clean it up right away.

Another example is when, say, your clothing in a low-humidity room becomes wet. You can expect mold growth if you don’t take care of it. In addition, any wet or cold surface can encourage mold spores to grow.

So, What’s the Ideal Humidity To Prevent Mold Growth?

According to the US Environmental Protection Agency (EPA), the ideal humidity level to avoid mold growth is below 60 percent RH (between 30 and 50 percent).

Maintaining humidity at that rate is critical. This is because mold spores require moisture to grow and thrive. Anything higher than 60 percent becomes an ideal indoor humidity range for mold growth.

How Would You Know if Your Home Has High Humidity Levels?

How Would You Know if Your Home Has High Humidity Levels

There are several key indicators that your home may have high humidity, including:

  • Musty odors
  • Condensation on your windows
  • Visible mold or mildew on the surfaces
  • Warped or swollen wood surfaces like walls and ceilings
  • Peeling paint off of the wall
  • Traces of dust mites
  • Sleeping issues
  • Severe allergic reactions

If you haven’t seen any of these signs, it’s always a good idea to keep track of the humidity levels in your home. You may consider getting a hygrometer, a handy device that monitors the relative humidity in the air. It may help you figure out whether the humidity levels in your house are safe.

Tips: How To Control Humidity Levels and Mold Growth

How To Control Humidity Levels and Mold Growth

Maintaining the proper humidity level in your house is essential for both comfort and health. Here are a few tips you can take to keep mold and mildew under control.

Ventilation Is Important

Adequate ventilation is the key when it comes to maintaining the ideal indoor humidity level in your home. Good ventilation, especially, is extremely crucial in humid areas or during particular seasons when the air is naturally moist.

In the summer, the air becomes naturally humid. Proper ventilation helps keep your house comfy while also keeping mold and mildew at bay. But if your home is very dry, good ventilation can help to bring in some fresh, moisture-rich air to help balance everything out.

Providing your home with good ventilation can be as simple as opening your windows and doors to let in the fresh air. You can also use a ventilation system like an exhaust fan.

Keep Areas Dry

But not too dry. While you want to avoid high levels of humidity indoors, you don’t want your home to be extremely dry that it hurts your skin. Low humidity can dry up your skin and irritate mucous membranes, resulting in difficulty breathing and potentially increasing your chance of becoming sick.

If you have wet surfaces, however, it’s always best to keep them dry. Spilling water on your linens, carpets, and rugs may seem trivial. But, it can escalate to something more serious, such as mold growth. If there is a leakage or a large spill, make sure to dry up as soon as possible.

Adequate Insulation

Good insulation is mold remediation worth investing in because it not only manages the temperature in your home but can also help control humidity levels.

In lower areas like your basement, insulation is particularly important. You must keep that part of your house as dry as possible. This is because ground moisture may enter the cellars and crawl spaces beneath your home. Given the environment, those damp places become a perfect environment for mold growth.

A good insulating system also helps regulate the flow of heat and moisture in your home and this can help maintain ideal humidity levels. In the winter, for example, insulation helps keep warm air in while creating moisture and helps control black mold.

During the summer season, it keeps your home cool by preventing extra moisture from accumulating. This can help keep humidity at a comfortable range.

Check Your Plumbing

Or better yet, check for any leakage. This is because pipes with leaks or cracks can add excess moisture to the air. It can be particularly damaging if the leak is in hidden or hard-to-reach places since it might go undetected for a long period of time.

Consider Moisture Absorbers

You may want to use moisture-absorbing materials to keep mold growth under control. Desiccants and silica gels can be great options to decrease black mold growth. But if you want something more natural, you can use charcoal briquette and put them in a vented container.

Using moisture-absorbing materials can also help improve air quality by reducing the amount of excess moisture in the air. And they can help preserve items in your homes such as paper and leather.

Invest in a Dehumidifier

A dehumidification system eliminates excess moisture from the air. It comes in very handy in basements and crawl spaces. As well as other areas where moisture is a problem.

This device is also particularly efficient if you want to prevent mold growth because they remove both the moisture and the source of the moisture. Make sure you opt for one that covers your floor space or just buy enough for every room in your house.

The best dehumidifiers for mold management are covered in our article here.


While there is no practical approach to getting rid of mold and spores, understanding the humidity levels at which mold is most likely to grow.

Moisture control and keeping the humidity levels at an ideal range are the keys here. So make sure you do regular inspections and quick correction of any moisture concerns. This way, you’ll be able to prevent mold growth and protect your family and your home.

You can also hire professional help to make the job easier. And don’t put it off until mold has already invaded your space.

Got more questions? Let us know!

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