Will a Dehumidifier Kill Mold: Keep Your Home Healthy and Mold-Free

By: Evan Scoboria, Last updated: June 28, 2023

Understanding how to combat mold in your home or office is crucial to maintaining a healthy indoor environment. Among various solutions, dehumidifiers are often recommended as an effective tool in this battle, but can they kill mold? Or are they merely preventive? In this article, we'll explore the relationship between humidity and mold and dissect the role dehumidifiers can play in managing these ubiquitous organisms. We'll also discuss the limitations of dehumidifiers and the additional steps required to tackle existing mold. By the end, you should have a comprehensive understanding of effectively using a dehumidifier as a part of your mold management strategy.

Mold Spore

Can a Dehumidifier Kill Existing Mold?

A dehumidifier does not kill mold. Mold is a fungus that grows and thrives in damp, humid conditions, but removing the moisture only halts its spread; it does not kill the existing mold spores. Dehumidifiers reduce the air's humidity level, creating a less conducive environment for mold to grow and multiply.

However, this does not mean that the mold present is eradicated. The mold spores can go dormant when conditions are not ideal, but they won't die off completely. The mold can start growing again once conditions are favorable (i.e., when there is enough moisture).

Understanding Mold and Its Causes

Mold is a fungus reproducing through tiny spores traveling through the air. These spores are microscopic and omnipresent in our indoor and outdoor environments. However, they become problematic when they find a hospitable environment to grow and multiply.

A mold-friendly environment is characterized by three main factors: moisture, a food source, and the right temperature. Moisture is the most critical factor, which can come from various sources like leaky pipes, roof leaks, flooding, high indoor humidity, or condensation on cool surfaces. The food source for mold usually consists of organic material, including wood, paper, carpet, food, and even dust.

Certain conditions, such as warm temperatures and poor ventilation, can further encourage mold growth. In the right conditions, mold can grow in as little as 24 to 48 hours and colonize a surface in one to twelve days. Once established, mold can be difficult to eliminate and cause various health issues, especially in individuals with mold allergies or compromised immune systems.

The Relationship Between Humidity and Mold

Humidity refers to the amount of water vapor present in the air. Molds are a form of fungi that exist naturally in the environment. They thrive in warm, damp, and humid conditions, often found in bathrooms, kitchens, basements, and other areas with high moisture levels.

Scientifically,  land on moist surfaces and multiply. When the relative humidity level in an indoor environment surpasses 60%, it creates optimal conditions for mold growth. This is because the water vapor in the air condenses on surfaces, providing the moisture that mold spores need to germinate and proliferate.

Moreover, the metabolic processes of mold involve the breakdown of organic matter (like wood, drywall, or any carbon-based material) and water absorption. When molds metabolize these materials, they release enzymes that break down complex molecules into smaller, soluble compounds that they can absorb and use for growth. If there's enough moisture present, the mold can continue this process, leading to visible and often destructive colonies.

The enzymes and mycotoxins produced by some molds can cause allergic reactions and other health problems in humans, so it's crucial to control indoor humidity and inhibit mold growth. Therefore, understanding the scientific relationship between moisture and mold is essential for maintaining a healthy indoor environment.

Types of Mold That Grow in a Home

Various mold species can find their way into homes, thriving in damp, poorly ventilated areas. Here are a few of the most common ones:

  1. Aspergillus: This genus comprises several hundred mold species and is often found in environments worldwide. It grows on various substances, including building materials and household dust. Some species can produce harmful mycotoxins and potentially cause human health problems, such as allergic reactions or respiratory issues.

  2. Cladosporium: This mold is ubiquitous in both indoor and outdoor environments and can grow on a wide range of materials, including textiles, wood, and painted surfaces. It's known for its dark, olive-green, or brown color. While Cladosporium is less harmful than other mold types, it can still cause allergies and exacerbate asthma symptoms in sensitive individuals.

  3. Stachybotrys Chartarum: Also known as black mold, this type is notorious for its potential health impacts. It usually grows on damp, cellulose-rich wood, gypsum board, and paper. Exposure to Stachybotrys chartarum has been associated with various health problems, including respiratory and allergic reactions.

  4. Penicillium: Known for its blue or green colonies, Penicillium is often found on water-damaged building materials and in soil. It spreads quickly and easily, and while it's best known for its use in penicillin, some species can produce harmful mycotoxins.

  5. Alternaria: This is one of the most common types of outdoor mold but can also be found indoors, particularly in damp areas like showers and under leaky sinks. It can cause allergenic reactions, particularly in individuals with asthma.

Remember, all these molds require moisture to grow. Hence, effective moisture control is a key strategy in preventing mold problems in your home.

The Role of Dehumidifiers in Mold Prevention

While a dehumidifier cannot directly kill mold, it can play a crucial role in preventing mold growth by reducing indoor humidity levels. A dehumidifier creates an environment less conducive to mold growth by extracting excess moisture from the air. Our research shows that 30% and 50% indoor humidity levels are optimal for preventing mold and maintaining a healthy indoor environment. These percentages are only a rule of thumb that we've developed, not a hard and fast rule. If, for instance, you are managing humidity around collectibles, a cigar humidor, or in a gun safe, you'll want to research appropriate humidity levels for that environment.

Additionally, dehumidifiers can be beneficial in cases of water damage, such as after a flood, leak, or spill. By speeding up the drying process, they can prevent the establishment and spread of mold.

Can Dehumidifiers Spread Mold?

No, dehumidifiers do not spread mold. On the contrary, dehumidifiers are commonly used to prevent mold growth by reducing humidity levels in the environment. High humidity levels, typically over 60%, create a conducive environment for mold growth. By lowering humidity levels to the recommended range of 30-50%, dehumidifiers create an inhospitable environment for mold.

However, if a dehumidifier is not cleaned and maintained properly, it could become a source of mold spores if mold growth occurs within the unit. Mold spores could then be blown into the room when the dehumidifier operates. Therefore, regular cleaning and dehumidifier maintenance are essential to prevent this.

Effective Mold Remediation Strategies

To effectively address mold issues, a comprehensive approach is required, including the following steps:

  1. Identify and address the source of moisture: This may involve fixing leaks, improving ventilation, or addressing other structural issues that contribute to excessive moisture.
  2. Remove existing mold: It's essential to clean or remove moldy materials, such as drywall, insulation, or carpeting, and appropriately disinfect affected surfaces using a mold-killing solution, like a mixture of water and bleach, or a commercial mold remover.
  3. Air filtration: Using an air purifier with a HEPA filter can help remove mold spores from the air, reducing the risk of mold-related health problems and preventing the spread of mold to other areas of your home.
  4. Maintain proper humidity levels: Use a dehumidifier, air conditioner, or other moisture control methods to maintain an indoor humidity level between 30% and 50%.

Limitations of Dehumidifiers in Mold Remediation

While dehumidifiers play a crucial role in mold prevention and can help create a living environment unfavorable for mold growth, they have certain limitations regarding mold remediation.

  1. Cannot Remove Existing Mold: A dehumidifier cannot kill or remove mold. While reducing the humidity can limit further growth, any existing mold colonies will remain and could continue to spread. The mold that has already taken hold must be physically removed, often by professional remediation services, and the underlying cause of the moisture problem should be addressed to prevent a recurrence.

  2. Limited Area of Effect: Dehumidifiers can only control the humidity level in a specific area, typically the room or area where the dehumidifier is placed. The mold growing outside the dehumidifier's reach, such as inside walls, crawlspaces, or large buildings, will not be affected.

  3. No Impact on Mold Spores: Dehumidifiers can't remove mold spores from the air. While lowering humidity can prevent these spores from growing into full-fledged mold colonies, it won't eliminate the spores themselves. Air purifiers with HEPA filters are required to effectively remove mold spores from the indoor air.

  4. Doesn't Address Underlying Causes: High indoor humidity can be a symptom of other problems, such as inadequate ventilation or leaks, which a dehumidifier can't address. Identifying and correcting these underlying issues is essential to prevent future mold growth.

  5. Maintenance and Cost: Dehumidifiers require regular maintenance, including emptying the water reservoir and cleaning to prevent mold and mildew formation within the unit. They also use electricity and can add to energy costs.

In conclusion, dehumidifiers are a valuable tool for maintaining a healthy indoor environment and preventing mold growth, but more is needed for mold remediation. They should be part of a comprehensive strategy that includes mold cleanup, addressing underlying moisture issues, and improving ventilation.

When to Seek Professional Help

If you're dealing with a severe mold problem or have concerns about the safety of mold removal, it's essential to seek professional help. A certified mold remediation specialist can assess the situation, identify the source of moisture, and develop an effective mold removal and prevention plan. As someone who's worked in the profession for many years, I can attest that most mold and moisture issues can be addressed with simple measures blocking moisture access and improving airflow. If you think mold impacts your home air quality, call a professional immediately before a small problem becomes significant.

Frequently Asked Questions

How does a dehumidifier help with mold control?
A dehumidifier helps control mold by reducing the humidity levels in your home. Mold thrives in moist conditions, and by reducing the moisture in the air, you create an environment where mold is less likely to grow.

Does a dehumidifier remove mold spores from the air?
A dehumidifier does not directly remove mold spores from the air, and its primary function is to reduce moisture levels, creating an unfavorable environment for mold growth. However, it does not kill or remove mold spores from the air.

How often should I run a dehumidifier to prevent mold?
The frequency of running your dehumidifier depends on several factors, including the humidity level in your home, the size of the space, and the specific model of your dehumidifier. In general, it's recommended to keep indoor humidity levels below 60% to prevent mold growth. Some dehumidifiers have a built-in hygrometer to measure humidity and adjust operation accordingly.

Can I use a dehumidifier in my basement to prevent mold?
Absolutely! Basements are often prone to high humidity and mold growth due to a lack of ventilation and frequent water leaks. Using a dehumidifier can help maintain optimal humidity levels and prevent mold growth.

Should I buy a dehumidifier immediately if I see mold in my home?
If you spot mold in your home, it's crucial to address the problem promptly. While a dehumidifier can help prevent future mold growth by controlling humidity levels, it cannot kill existing mold. You may need a professional mold remediation service to remove the mold safely.

How effective are dehumidifiers in mold-infested areas?
Dehumidifiers can effectively prevent mold growth in areas with high humidity. However, they cannot remove or kill existing mold. Professional remediation will be necessary if an area is already infested with mold.

Do I still need professional mold remediation even if I have a dehumidifier?
Yes. Professional mold remediation is recommended for visible mold or a large infestation. Mold can be hazardous to your health, and professionals have the proper equipment and knowledge to remove it safely.

How do the size and capacity of a dehumidifier affect mold prevention?
The size and capacity of a dehumidifier can significantly impact its effectiveness in controlling humidity and preventing mold. Larger spaces or areas with high humidity levels may require a larger, more powerful dehumidifier.

Are there other ways to prevent mold apart from using a dehumidifier?
Yes, other measures can help prevent mold. These include improving ventilation, fixing leaks promptly, drying damp areas quickly, and cleaning regularly. Proper insulation can also help control humidity levels in your home.


In conclusion, while dehumidifiers play an integral role in maintaining optimal humidity levels and creating an environment less conducive to mold growth, they cannot be relied upon as a singular solution for mold remediation. They cannot kill or remove existing mold, impact mold spores, or address underlying moisture problems, which are often the root causes of mold infestations.

Moreover, their effectiveness is confined to a particular area, and they require regular maintenance and can add to energy costs. Therefore, their usage should form part of a broader mold prevention and remediation strategy, which may include professional mold removal, addressing any sources of excess moisture, and improving indoor ventilation. Maintaining a balanced approach to indoor humidity is vital, taking care not to let levels drop too low or rise too high to ensure a healthy and comfortable living environment.