Pink Residue in Humidifier: What You Need to Know

You’ve been enjoying your humidifier for several months, and feeling fantastic from the benefits it gives you.  After all, humidifiers can:

  • Help you sleep better.  Keeping your room’s air circulating with moisture helps you breathe better, which can help you get a better night’s sleep.
  • Relieve symptoms of allergies.  Stuffy noses, sneezing, irritated eyes, itchy skin and throat; these are all issues you may experience with allergies.  Using a humidifier can help soothe these symptoms, so you don’t have to suffer.
  • Ease cold and flu symptoms.  Coughing, chest congestion, and nasal irritation can make you feel miserable, and it always seems to worsen at night.  Using a humidifier can help alleviate these symptoms and help you get the rest you need to get better, faster.
  • Keep skin and lips moisturized.  Dry air dehydrates skin and sensitive mucous membranes like lips.  Using a humidifier can help keep skin and lips hydrated and comfortable.   

While you’re enjoying your humidifier, you may have noticed one tiny little problem: slime!  

Maybe you noticed it the first time you opened the water reservoir tank to refill it--a thin layer of slimy “gunk” on the bottom edges and sides of the water tank.  Over time, this slime can actually turn colors.  The next time a refill is needed, you’re hit head on with a pink substance that looks slightly like a science project!  

This slime can also collect on the spout where your humidifier releases water vapor into the air.  This can be incredibly alarming and make you think twice about turning it on again.  Thankfully, this residue is common, normal, and easy to remedy. 

Let’s look at what it is, why it happens, and how to get rid of it.  

humidifier in the bathroom

What is Pink Mold?

Mold comes in many colors, like a beautifully disgusting rainbow.  While the most common types of mold you will likely see in your home range from green to black, mold also comes in varieties of orange, pink, purple, brown, and even red.  If you’re really lucky, you may even have a combination of these colors.  

Pink mold is the most common type of mold found in humidifiers.  Pink mold infamously grows in areas that are damp to wet and dark, making the water tank of your humidifier a prime location for this mold to hang out.  Even if your water tank is clear, pink mold will likely form inside, because the water in the tank sits overnight when it is dark in the room where your humidifier is located.  

There are essentially three types of pink mold:

  • Serratia marcescens (S. marcescens).  This type of pink mold isn’t actually a mold at all, but rather a form of bacteria.  This is most commonly found in bathrooms around sinks, showers, and toilets.  This bacteria feeds on ingredients found in soaps and shampoos, which makes your bathroom a virtual fairground for its development.  You can help eliminate this type of bacterial growth by rinsing down your showers and sinks when you’re done to eliminate soap and shampoo residue.
  • Aureobasidium pullulans (A. pullulans).  This mold is also common in bathrooms, but will also form on organic materials like plants and wood.  It can start off white or yellow, but eventually turns to pink.
  • Fusarium.  You will likely not ever deal with this type of mold in your home.  This mold grows on organic, plant-based material and can then spread to nearby surfaces.  As such, you would most likely find this type of mold near a house plant and/or on wall and carpet space near the plant. 

If you’re seeing pink mold in the tank or in other parts of your humidifier, you are likely dealing with A. pullulans.  This type of mold is relatively harmless, but can cause some negative side effects when exposure occurs over a long period of time (like extended use of a humidifier that hasn’t been properly cleaned).

How Does Pink Mold Form?

If you’re wondering how this stuff got inside your humidifier in the first place, don’t worry.  The development of mold inside of a humidifier is almost inescapable and has nothing to do with your level of cleanliness or housekeeping.  

Your humidifier works by holding water (which may or may not be purified) in a tank.  When in use, the humidifier pulls water from that tank and sprays it into the air in the form of water vapor.  Because humidifiers are used frequently overnight to help you sleep better, it is not surprising that the dark, damp interiors of the tank and spout become targets of bacteria and mold.  

Pink mold can begin forming within 24-48 hours of humidifier usage.  Whether or not your humidifier will develop mold can depend on the level of bacteria already present in the humidifier, and whether or not the water in the tank has been distilled.

Is Pink Mold Dangerous?

Pink mold isn’t inherently dangerous, and you don’t need specialized equipment to deal with it, nor do you need to call in a HAZMAT team to clean your small appliance.  However, over time, exposure to pink mold can cause respiratory problems.  If you don’t remove the pink mold from your humidifier, you are giving the mold an opportunity to be sprayed out into the air along with the cool mist vapor.  

When this happens, mold that is expelled from the humidifier looks for a new space to invade, and that place can oftentimes be your nose and lungs.  This can lead to a condition called “humidifier lung.”  This condition leads some people to believe that using a humidifier is dangerous, but it really has nothing to do with the humidifier at all, and everything to do with its improper cleaning.  

Symptoms of humidifier lung are similar to that of a cold; difficulty breathing, coughing and congestion, and fever.  

The best way to avoid an issue with pink mold is to regularly inspect and clean your humidifier.  With proper care, you will never have to worry about becoming sick from your humidifier.  

How to Clean Pink Mold from a Humidifier

Regular humidifier cleaning and maintenance should be performed every time you refill your humidifier with water, or roughly once a week.  This level of cleaning and attention should be enough to keep your humidifier from developing pink mold in the first place.  

If your humidifier is mold-free, you can clean it in 5 simple steps.

  • Unplug your unit and remove the water basin from the humidifier and empty any remaining water.  
  • Use a mild soap and clean sponge to clean the inside of the water basin. 
  • Dry thoroughly and replace.
  • Inspect the vapor spout to ensure there is no growth of mold. 
  • Use a mild cleanser and a clean rag or paper towel to clean the vapor spout.

If your humidifier has developed pink mold, you can easily clean it and restore it to proper use.  You should always follow your humidifier’s manufacturer’s instructions for cleaning.  

If your manufacturer’s instructions allow, you can clean your humidifier and the mold in it by following these steps:

  • Unplug your humidifier and remove the tank from the base.  
  • Fill the water tank with either vinegar or hydrogen peroxide.  You can use a chemical ingredient, like bleach, but it really isn’t necessary, and depending on your manufacturer's instructions, could be potentially hazardous to the machine.  
  • Allow the vinegar or peroxide to sit in the tank for about half an hour.  This gives it time to break down the pink mold so it can be easily removed.
  • Empty the peroxide or vinegar from the tank and rinse with warm water.  
  • Dry thoroughly.  
  • Clean the base by carefully following your manufacturer’s instructions and using a solution of water and peroxide and/or water and vinegar.  
  • Inspect the vapor spout.  If it has developed mold, you can use the same solution of vinegar or peroxide and a toothbrush to scrub away the buildup.  

humidifier in the bathroom

Proper maintenance and cleaning of your humidifier should be enough to keep pink mold at bay and keep you and your family safe.  You can also take measures to prevent pink mold by avoiding the use of tap water and opting for distilled water for the humidifier instead.  If you have hard water, the minerals may make your humidifier more susceptible to mold and bacteria development than distilled water, so making the switch could be very effective in helping you keep your humidifier clean.

If your manufacturer allows it, you can also add a small amount of vinegar to the water in the water tank of your humidifier, which can help keep the tank from developing pink mold.   


Pink mold in a humidifier is a really common occurrence and can be easily removed by simply giving your humidifier a good cleaning.  You can prevent the development and buildup of pink mold by routinely inspecting and cleaning your humidifier, and by opting to use distilled water instead of tap water in your machine.  

Pink mold can be harmful if left untreated, so it’s important to take measures to ensure the timely removal of pink mold inside your humidifier so the mold does not have an opportunity to be dispersed from the humidifier along with the cool mist vapors.  


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