Bathroom High Humidity – Its Causes and How to Solve It


Controlling humidity in a bathroom can be quite a challenge, but it’s possible.

So, what can you do about high humidity in your bathroom? You’ll have to have methods in place to remove moisture from the air like a dehumidifier and exhaust fan, as well as control temperature and the amount of organic material present to prevent mold growth.

Let’s take a look into more detail and the actionable steps you can take to reduce the humidity in your own bathroom.


Why High Humidity Is a Serious Problem

Humidity is perfectly normal after taking a shower, but if the excess moisture is allowed to linger and deposit on the surfaces, it can become a major problem eventually.

A mold problem, to be exact.

Mold thrives in warm temperatures between 77 and 86 °F and relative humidity (RH) levels above 60%.

Mold feeds on organic matter on bathroom surfaces like:

  • Wood surfaces
  • Carpet
  • Ceiling tiles
  • Skin flakes and hair
  • Cotton towels, pillows and curtains
  • Glue behind peeling wallpaper
  • Cellulose-based building materials like exposed drywall and insulation

Once mold forms, it can be difficult to eliminate since it only takes one spore for it to multiply again, sooner or later.

If left unchecked, mold can cause severe coughing, wheezing, and other general irritation of skin and mucous membranes. Mold can also worsen asthma symptoms.

Not only can mold eat away at wood, carpet, and building materials, but it can also get into your HVAC system and grow there, becoming even more costly to fix. So not only would you have to dish out thousands of dollars for a professional mold remediation, you’ll have to do the same to replace ductwork and a damaged HVAC unit.

Not to mention that the HVAC system can then also spread mold spores to other parts of the home for years, including bedrooms and nurseries, so there is a high cost to health as well.


High Humidity Solutions for Your Bathroom

Now that you know why high humidity matters, let’s take a look at actionable solutions.



The Environmental Protection Agency (EPA) recommends to keep RH levels between 30% and 50%, although in a bathroom it can be difficult to do sometimes. Get an inexpensive hygrometer to first measure how much humidity your bathroom has, then buy a dehumidifier that matches the need. Here’s a reasonable one from Amazon.

It’s a good idea to assess the situation first before investing in a dehumidifier. Homeowners notoriously buy dehumidifiers that are too small for the space, which usually has to do with how dehumidifiers are rated.

If in doubt, buy a dehumidifier that’s rated for a greater square footage and is energy-efficient. Some very small bathrooms may also be helped by silica gel desiccant dehumidifiers like the Eva-Dry.

Otherwise, I recommend this post to find a dehumidifier that’s going to be effective enough.


Ventilation and Exhaust Fans

Unless you want your dehumidifier to run non-stop and drain your electricity bill, you’ll have to pay attention to the ventilation in your bathroom.

Ventilation helps move the air, so that mold spores have less of a chance to deposit on organic surfaces. Ventilation helps keep surfaces dry and reduces condensation, which is especially important in damp bathrooms.

But how do you choose the right bathroom exhaust fan?

Besides checking to make sure that the exhaust fan is venting to the outside properly, a few factors you’ll need to look at are:


Air Change Rate

Because a bathroom is prone to sudden temperature and moisture changes, it must be ventilated quickly to get it back to normal. After all, you definitely don’t want your walls absorbing moisture for hours after you take your shower.

A good exhaust fan must be capable of cycling the air in the bathroom quickly, and the rate at which is can change out all the air in a given amount of space is known as the air change rate. This is measured as CFM, or cubic feet of air that can be changed out per minute.

It’s recommended that a bathroom exhaust fan be able to change out the air 8 times per hour.

Say you have a bathroom that’s 10′ by 12′, assuming you have a flat 8′ ceiling throughout. That’s 120 square feet of space, or 960 cubic feet of volume.

If we want the air to be changed out 8 times per hour, that’s 7,680 cubic feet that must be moved. Divide this by 60 to convert from hour to minute, and you’ll come up with a 128 CFM bathroom exhaust fan.

If you don’t want to do the math, a general rule of thumb is 1 CFM per each sq. ft. of area. Although, you shouldn’t forget to take other things like high or cathedral ceilings, wall separations, and additional plumbing fixtures into consideration as well when deciding how powerful the fan needs to be.


Noise Control

Bathrooms logically are adjacent to bedrooms, so an exhaust fan can be quite noisy at night when we try to sleep.

The amount of noise that bathroom exhaust fan emit is measured in sones. A fan with a sone rating of 4 will be quite noisy, while one that only has a rating of 0.5 is barely audible.


Humidity Sensors

Exhaust fans nowadays have advanced features like humidistats, or humidity sensors. This fan can turn on automatically when relative humidity surpasses a certain level, usually 60% (if you can set it below that, it will be even better against mold).

Many are quite versatile, allowing you to adjust both the CFM and humidity level threshold at which the fan should turn on. Like the Delta exhaust fans, for example.


Best Practices and Minor Solutions

Here are a few tips that can visibly reduce humidity once combined.


Vent any appliances that produce water.

If you keep a clothes dryer or kerosene heater in or near your bathroom, make sure they’re properly vented to the outside. In fact, anything in your home that combusts not only can give off carbon monoxide if not improperly vented, but it can also give off water vapor.


Don’t dry anything in the bathroom.

Taking a step further from the above precaution, it’s better to not even dry anything in the bathroom in the first place. Take out any towel drying racks and wet towels out of the bathroom and do the drying in another area of your home.


Keep organic material out of the bathroom.

If doing a renovation, you can swap out your wood cabinets, surfaces, paint, and fixtures for other materials that will hold up better against moisture and mold. Wood species like cedar, black cherry, and white oak hold up well against moisture.

If your wallpaper is starting to peel off, it’s time to replace it. Not just because it’s old and doesn’t look nice, but also because mold will feed on the exposed adhesive.

Some wood and paint products are also treated with fungicide at the factory. This includes Frame-Guard wood products, Nu-Wool insulation, and Zinsser paint. Drywall that has a fiberglass face instead of paper will also absorb less moisture and stave off mold spores.

Just make sure at least some of the products are GreenGuard-certified to ensure they don’t off-gas excessive chemicals once installed in your home.


Wipe wet surfaces down after showering.

Water droplets can linger on bathroom tiles for hours after showering, so it’s important to take care of this as soon as you take a shower.

Wipe down any excess moisture off the floors and surfaces immediately after showering. Squeegees are a great way to do this.


Take cooler and shorter showers.

Mold thrives on warmer temperatures, so taking cooler showers will help alleviate the problem. Make your showers short as well.


Declutter your bathroom from beauty and hygiene products.

Shampoo and body wash bottles are just additional surfaces for water droplets to accumulate and mold and bacteria to grow on. Keep only what’s necessary in your bathroom, and keep everything else on hand in a nearby (dry) closet.

Throw out all products that have been in the bathroom for years. Shampoo and lotions tend to have preservatives that can somewhat thwart off fungi and bacteria, but only if they’re not past their expiration date.


Clean with bleach regularly.

Bleach can thwart mold growth. Go beyond cleaning the tub, sink, and toilet only – dilute some bleach and clean walls, baseboards, and inside cabinets as well to prevent mold and mildew growth. Even better, look for mild household cleaners with fungicide in it.



Keep organic fabrics to a minimum.

Change out your cotton shower curtain for a plastic liner only, or buy one that’s marketed as mildew-resistant. Take out any pillows that are sitting on window benches, as well as decorative towel displays that aren’t being used. Remove or wash rugs more often. All these are invitations to moisture retention and mold growth only.


Crack open the window when showering.

The best way to get moisture out and to change out the hot and humid air in a bathroom is as simple as cracking a window open when showering.


Check your HVAC ductwork.

Ventilation is key, so make sure your HVAC ducts are clean and the filters are changed out regularly. Blocked ductwork can allow condensation to form as the hot water cools from your shower.

Remember, mold can grow inside ducts as well, so it’s wise to maintain the HVAC system.


Open the bathroom door after showering.

Rather than confine the moisture to the bathroom alone, open the door after showering to allow the moist air to dissipate and mix with the cooler, dryer air in the rest of your home.


Check your plumbing fixtures for minor drips.

Not all plumbing issues need to be alarming. Sometimes the problem can be as simple as a loose faucet that causes minor dripping, and it can be a simple DIY project if all you have to do is replace an O-ring or washer.

Don’t forget to check under the sink as well. If the faucet has been dripping for a while, it’s possible that the wood cabinets underneath have started to rot, creating the perfect environment for mildew and mold to thrive.


Seal any surfaces where water or mold can enter.

Clean out the grout between the tiles, then apply sealer to them. It’s possible that your counter top and wood surfaces may need a fresh coat of sealer, too. Remove old caulking and reapply new caulking again.



There are many ways to reduce humidity in a bathroom. It primarily has to do with keeping the bathroom well-ventilated and having a bathroom exhaust fan that’s powerful enough for the size of the bathroom.

In addition to that, some “best practices” should be implemented, like wiping surfaces down after showering, keeping the amount of organic materials out or clean, for example.


Related Questions

How much do I dilute the bleach when cleaning, and are there other solutions?

It depends, but generally you rarely should want more than a third bleach and two thirds water. Even that is a bit high by some standards. Contrary to popular belief, a more concentrated bleach solution doesn’t necessarily give much greater results. A little will go a long way, and if you don’t want to use bleach, consider a distilled white vinegar or baking soda solution. Some people also like to use Borax, although I personally am not a fan of it.


What if I have a small bathroom and no room to fit a portable dehumidifier?

If you’ll be replacing your exhaust fan anyway, then just get one that has higher CFM that recommend. That should help with the dehumidification process. Supplement it with plug-in or wireless silica dehumidifiers like Eco-Dry that you can scatter throughout. Also, consider mini dehumidifiers that can be discreetly tucked away near the toilet, or can be placed on an extended counter top surface.

Desiccant dehumidifiers will also probably be a better solution compared to a traditional compressor dehumidifier for you, and can go beyond the size of the smaller Eva-Dry dehumidifiers. They’re generally half the weight of compressor dehumidifiers and will give you more ability to slightly move them around.

If you must buy a larger unit and the dehumidifier will be placed on the floor, look for those with casters to give you more versatility.