Pink Mold In Humidifier: It's Causes and Remediation

By: Evan Scoboria, Last updated: June 23, 2023

The slimy pink residue that we often call "pink mold" isn't mold at all but a type of bacteria. If you've noticed a pinkish residue in your humidifier, you're probably dealing with either Aureobasidium pullulans or Serratia marcescens, both of which thrive in moist environments. In this article, we delve into what these bacteria are, their potential risks, and, most importantly, how you can clean and prevent them in your humidifier.

Pinkish residue in a humidifier

What Causes Pink Mold in Humidifiers

The "pink mold" you may find in your humidifier is often not a mold but a type of bacteria. Humidifiers create an environment with plenty of moisture, which can be a haven for bacterial growth. Two types of organisms are primarily responsible for this pink residue:

Aureobasidium pullulans

Aureobasidium pullulans is a yeast-like fungus in various environments, including soil, water, and air. It is often associated with plants and can be found in the phyllosphere, the above-ground parts of plants. It is known to be a common indoor mold and is usually black but can sometimes appear pinkish. In humidifiers, Aureobasidium pullulans result in a pink or black discoloration, often mistaken for "mold." 

Aureobasidium pullulans have significant industrial importance. It can produce various enzymes and polysaccharides with potential applications in multiple industries, such as food, textiles, and paper. For instance, it can produce pullulan, a polysaccharide used in the food industry as a thickener and adhesive, and for its ability to form films and fibers.

Despite its usefulness, Aureobasidium pullulans can also cause problems. It can be a contaminant in indoor environments and can potentially cause health issues such as allergic reactions. Specifically, it is known to cause Type I allergies (hay fever, asthma) and Type III allergies (hypersensitivity pneumonitis). This is often seen in individuals with a weakened immune system or prolonged exposure to this organism.

Serratia marcescens

In humidifiers, the warm, moist environment can provide ideal conditions for the growth and proliferation of Serratia marcescens, which may result in a pink biofilm or residue. This pink slime is often mistaken for "pink mold." While it can be disconcerting, regular and thorough cleaning of your humidifier can prevent its growth and the potential for respiratory issues, especially in individuals with weakened immune systems or lung diseases. You should always follow the manufacturer's instructions for cleaning and maintaining your humidifier.

Serratia marcescens is a rod-shaped, gram-negative bacteria in the family Enterobacteriaceae family. This bacterium is commonly found in environments such as soil, water, and even in the digestive tract of some animals, including humans. It is known for producing a distinctive red pigment, especially when grown at lower temperatures, which gives it a reddish or pinkish appearance.

The most notable trait of Serratia marcescens is its potential as an opportunistic pathogen. It can cause various human infections, particularly in hospital settings where it can take advantage of immunocompromised patients. Conditions can range from urinary tract infections, wound infections, and respiratory tract infections to serious systemic diseases like sepsis.

Is Pink Mold in a Humidifier Dangerous?

While the term "pink mold" may be a misnomer, as bacteria, not mold, typically cause the pink residue often found in humidifiers, it can nonetheless pose health risks. As mentioned earlier, the main culprits are Serratia marcescens and Aureobasidium pullulans, which can potentially cause human infections.

Exposure to these bacteria may not cause noticeable health effects in healthy individuals. However, exposure could lead to respiratory infections or exacerbate conditions for individuals with weakened immune systems, pre-existing respiratory conditions, or allergies. Moreover, prolonged exposure to these bacteria, even for healthy individuals, can lead to respiratory issues.

It's also worth noting that while pink residue in a humidifier is not desirable, the potential health effects largely depend on the extent of contamination and the duration of exposure. A small amount of pink residue noticed and promptly cleaned is less likely to cause health issues than a humidifier with significant bacterial growth operating for an extended period.

Regular cleaning and maintaining your humidifier is always advisable to prevent the growth of these bacteria. Also, if you notice a pink residue forming in your humidifier, it is recommended to clean the humidifier thoroughly before using it again.

How to Clean Pink Mold from Humidifier

Cleaning pink residue, often mistaken for mold, from your humidifier involves several steps that require careful attention to ensure a thorough job. You can start by unplugging the humidifier from the power source for safety.

Drain the Humidifier

Remove the water tank and empty any remaining water. You should also drain any water from the base of the humidifier. 

Clean and Disinfect 

Using a solution of one part white vinegar to one part water is a good start. This solution can be used to clean the base and tank of the humidifier. Vinegar is a great natural cleaner that can effectively kill bacteria and dissolve mineral deposits. Fill the water tank with the vinegar solution, swish it around, and let it sit for about half an hour. Also, soak the humidifier's base in the vinegar solution if possible.

In the meantime, take a clean cloth or sponge dampened with the vinegar solution and wipe down the exterior of the humidifier and any other parts you can reach. For small or difficult-to-reach parts, use a small brush or cotton swabs.

Once the vinegar has had time to sit, thoroughly rinse all parts of the humidifier with clean, warm water to ensure all traces of vinegar and any dissolved deposits are removed.

Dry Thoroughly 

Then, wipe down all parts with a dry cloth and let them air dry completely. This is crucial, as any remaining moisture can encourage bacterial growth.

How to Prevent Pink Mold in Humidifiers

Using distilled or demineralized water instead of tap water can also help to prevent bacterial growth. These types of water have had most, if not all, of their mineral content removed, which deprives bacteria of a critical nutrient source.

Finally, remember to empty the humidifier when it's not in use. Stagnant water left in the tank or base can rapidly become a breeding ground for bacteria and fungi. Keeping your humidifier clean, dry when not in use, and filled with distilled or demineralized water can significantly reduce the chance of pink bacteria or mold appearing.

Frequently Asked Questions

Is pink mold dangerous?
Pink mold is not a mold but a bacteria called Serratia marcescens. While it's generally not harmful to healthy individuals, it can lead to respiratory and urinary tract infections in those with weakened immune systems.

How do I clean pink mold from my humidifier?
To clean pink mold from your humidifier, use a solution of equal parts white vinegar and water to scrub all parts of the unit. Then, rinse with clean water and dry thoroughly. A soft brush or cotton swab may be helpful for smaller pieces or hard-to-reach areas.

How can I prevent pink mold in my humidifier?
Preventing pink mold in your humidifier involves regular cleaning every two to three days, using distilled or demineralized water, and thoroughly drying the unit before storing. It's also a good idea to empty the humidifier when not in use to prevent water from stagnating.

Does pink mold only grow in humidifiers?
No, pink mold can grow in any damp environment that is not regularly cleaned. This includes bathrooms, kitchens, and laundry rooms.

What are the health risks associated with Aureobasidium pullulans and Serratia marcescens?
Aureobasidium pullulans can cause infections in immunocompromised individuals. Serratia marcescens can lead to respiratory and urinary tract infections, particularly in hospital environments or among those with weakened immune systems.


In conclusion, the pink mold in your humidifier isn't mold but bacteria like Aureobasidium pullulans and Serratia marcescens. While these bacteria generally pose a low risk to healthy individuals, they can lead to respiratory and urinary tract infections in those with weakened immune systems. It's crucial to clean and maintain your humidifier regularly to prevent these bacteria from proliferating. Preventive measures such as using distilled or demineralized water, regular, thorough cleaning, and drying out the humidifier before storage can help keep your humidifier free from pink mold and ensure the air you breathe is as clean and healthy as possible.