How to Do a Cloth Diaper Swish Test for Detergent Build-Up

By April Duffy •  Updated: 05/03/24 •  11 min read

I’ve written about detergent build-up cloth diapers before. In my post about the problem with Fluff Love University detergent index recommendations, I talked about Emma, a first-time mom who invested in cloth diapers to save money. Like so many of us cloth diaper users, Emma had no friends and family to support her, let alone offer guidance, so she had to turn to the internet for wash and care advice.

Pretty quickly Emma found what looked to be an awesome resource, the Fluff Love University (FLU) Detergent Index, which gave her an almost complete list of detergents, told her which were good and which were bad, and even gave her the amount to use for each detergent listed. 

Emma was impressed with all the work that went into that site and the attention to detail. She also wanted to prove all of her naysayers wrong. Determined to succeed, she followed the FLU instructions to the letter. This is why Emma was so confused when her diapers began to stink and her baby started to get rashes. 

Emma felt like a failure, but the truth was that it was unavoidable given the advice she received.

A lot of the advice cloth diapering beginners get online around washing cloth diapers today, especially on Facebook, leads to detergent residue buildup problems.

Advice like:

While I’m certain it’s all well-intentioned advice, the truth is that it leads to failure from detergent residue build-up.

So, Do You Have Detergent Build-Up in Your Cloth Diapers?

If you’ve used Fluff Love University detergent recommendations in the past, purchased used diapers, are using a water softener with your laundry, or are having smell issues you can’t seem to solve, it’s very possible you have detergent build-up in your cloth diapers. I recommend testing your cloth diapers for detergent build-up if any of those scenarios sound like you.  

I will get into how to test your diapers and how to read the results soon enough, but first, let’s dive into why you need to solve detergent build-up ASAP.

Why Is Detergent Build-up so Bad? 

While Fluff Love University claims detergent build-up is a myth, I am constantly helping moms deal with the stink and rashes that come from it. As soon as the detergent (visible through suds) is gone, so is the stink and rash problems. It’s also well known to be a problem by the detergent industry itself. 

As Mary Gagliardi, a scientist at Clorox, explains in this Readers Digest article, using too much detergent can lead to a ton of problems including stains and residues on clothes, smelly washing machines, wetter clothes at the end of the cycle,  increased wear and tear on your washer’s pump and motor, and of course an increase in the bacteria left on your laundry. 

Much of the problem is that too much detergent in your washer causes too many suds. 

Tide’s website states that:

“Too many suds prevent a good wash by cushioning the clothes from rubbing against one another – it’s this rubbing that helps the clothes get as clean as possible…. Not only does oversudsing affect your washer’s efficiency, but excess suds can also prevent some of the impurities from being completely rinsed out of the machine properly. This means that impurities can redeposit onto your clothes, resulting in odors or machine malfunctions. 

“Too many suds can also block up the system, which can prevent the washer from pumping out water and, in turn, cause more suds.”

Too Many Suds in the Washer.

It’s both the re-depositing of bacteria and feces/urine onto your cloth diapers and the detergent particles still on your diapers that can cause irritation to skin, and of course that tell-tale ammonia stink

Should My Cloth Diapers Smell Like Detergent?

While ammonia smell is absolutely an early warning sign of detergent residue, there’s also another smell to be slightly concerned about — a strong detergent scent.

Should clean cloth diapers should smell like detergent out of the wash? Not usually. Out of the wash, your cloth diapers should just smell clean. A super-strong detergent scent could mean that your detergent isn’t all being cleaned away and it’s being left on the surface of the cloth diaper, which is the start of build-up.

Of course, this can vary by brand as some brands, like Gain, for example, put extra fragrances in to mask smells. Even with those high-fragrance brands however your clean diapers shouldn’t smell strongly of detergent.

A strong detergent smell is a good reason to test for detergent build-up just to be safe.

How to Test for Detergent Build-up: The Swoosh Test

Of course, not all rashes and stinky cloth diapers are caused by detergent build-up. Products like petroleum and zinc, fabric softeners, and infrequent washing (leading to bacteria build-up) can all cause your diapers to not get fully clean and thereby start to stink and harbor bacteria. 

Diagnosing the problem is an important step to solving it since the remedy for removing detergent buildup and the remedies for product buildup or still-dirty diapers are different.

Here’s how to do a swoosh

  1. Fill up a glass bowl with warm water
  2. Submerge a clean and dry diaper in to the bowl
  3. After a few minutes swoosh it around and squeeze it out a few times.
  4. Remove the diaper and read the results.

That’s it.

Reading the Swoosh Test Results (with Pictures)

Reading the results of a swoosh seems simple enough, if white film and/or heavy bubbles (suds) gather along the sides of the bowl, it shows buildup. But in practice, I’ve noticed that the sight of any mild haze or cloudiness in the water has caused a lot of Cloth Diapers for Beginners community members to panic. And while I understand the concern, not all bubbles are a sign of impending doom. 

Sometimes, that slight haze is just dirty diapers (caused by product buildup or not enough detergent in your wash), and those bubbles could be harmless air bubbles that will dissipate in a few minutes.

A true case of detergent build-up will present itself as a white film and/or persistent suds that gather along the sides of the bowl.

To make it clearer and help you do your swoosh tests with confidence, I have some photos of example results to help you read your own swoosh tests.

Example Results: No Detergent Buildup

Negative Cloth Diaper Swoosh Test.
Cloth Diaper Swoosh Test with No Detergent Buildup

Example Results: Detergent Buildup Moderate and Heavy

Positive Cloth Diaper Swoosh Test.
Cloth Diaper Swoosh Test with Detergent Buildup.
Cloth Diaper Swoosh Test showing Moderate Detergent Buildup.
Cloth Diaper Swoosh Test Showing Heavy Detergent Buildup.

Example Results: Detergent Buildup vs. Air Bubbles

One of the most confusing negative results can be the air bubbles caused by swooshing in soft water. Often big, airy bubbles will form when you agitate exceptionally soft water and they can actually stay along the top of the water for a while. This makes reading slight detergent buildup even harder.

You can tell the difference by waiting a while after you’ve swooshed your cloth diaper and looking first for the tell-tale detergent ring around the side of the bowl.

Cloth Diaper Swoosh Test: Detergent vs. Air Bubbles

How to Remove Detergent Build-up For Good

If you do find yourself with a detergent build-up problem, you’ll want to take the following three steps to fix the problem and reset your cloth diapers:

1. Clean Your Washing Machine

Unfortunately, if you’ve been regularly using too much detergent, it’s most likely that not only do your cloth diapers have detergent build-up on them, but you have detergent residue lining your washing machine as well. 

In fact, if you’re only following the recommended amounts on the detergent bottle for your diapers, and using too much in your regular laundry, the problem could very well just be with your machine having build-up that’s depositing on your cloth diapers.

Recall the Tide website said that too much soap can block the system, preventing the washer from pumping out water and, therefore causing more suds.

How to Get Rid of Suds in Washing Machine

To clean your washing machine, you can use a commercial cleaner like Affresh (Amazon Link), or simply run a full cycle (some machines do have self-cleaning cycles) with hot water and a cup of vinegar to cut through the detergent. 

This of course only applies if you’re using the same machine all of the time. If you’re using a commercial laundromat or traveling etc. this step will be fruitless for you. 

2. Rinse Your Diapers Clean

Once your machine is clean, it’s time to tackle the diapers themselves. The detergent that’s built up on them needs to be cleaned away completely. The quickest way to do this, though it can take some time, is to rinse them until the water runs clear.

Again, this can take some time. I once coached a mom though having to rinse out so much build-up it took 14 rinse cycles and two strips to remove it all!

Should You Strip Your Diapers to Remove Build-up?

In the past, I’ve recommended stripping your diapers to help remove detergent residue but after coaching literally thousands of parents through the process I’ve found it’s largely unnecessary and sometimes can delay things. Rinsing the diapers thoroughly, perhaps using some vinegar in the rinse (you can read all about vinegar for cloth diapers here), is often the best and fastest remedy (even though it can take some time).

If however, you’re removing buildup from used diapers, and are skeptical that there may be other build-up on the diapers—like fabric softener or diaper creams—stripping can also be done. You can read my full post about how to strip diapers here.

After doing a strip you’ll still likely need to rinse them and continue rinsing until you don’t get any suds through either of the tests mentioned above, this could take several rounds of rinse and spin cycles or time spent at a faucet rinsing and squeezing until the water runs clear.

3. Adjust Your Wash Routine 

Once everything is clean, adjusting your routine is crucial to prevent the problem from recurring.

The Measure Method of washing cloth diapers helps you work out how much laundry detergent is appropriate for the amount cloth diaper laundry you’re washing at a time, your water hardness, and your preferred cloth diaper detergent. It also makes sure they don’t overload your washer with too many diapers. An overloaded machine, especially a high-efficiency washer made to use very little water and power, won’t add enough water to the cycle to fully rinse detergent away.

Taking the time to balance your dirty cloth diaper wash routine can seem like a daunting task at first, but it’s so much easier than having to rinse out detergent buildup and remedy diaper rashes.


Laundry detergent residue from using too much detergent is very much a real problem and even acknowledged by detergent makers themselves (see quotes from Clorox and Tide above).

When detergent residue sticks onto a cloth diaper, the dirtiest and most multi-layered laundry you’ll ever wash, it causes more problems than dull and stiff fabric, it causes bacteria build-up, stink issues, and eventually rashes. It can also be very bad for your washer. 

To test for detergent build-up you can either test a single clean diaper in a bowl of water or perform an extra rinse in your washer as laid out above. If you’re using multiple washing machines or a laundromat to wash your diapers, the swoosh test of a single diaper will be best for you. 

If you find that you do have detergent build-up you’ll need to reset your washer and your diapers by cleaning them thoroughly. Once you’re back to ground zero, you’ll need to adjust your wash routine to keep the buildup from happening again. I recommend the Measure Method for cloth diaper laundry, which I outline here.  

April Duffy

April is the founder of Cloth Diapers for Beginners and author of The Cloth Diaper Wash & Care Handbook. Since 2015, April has helped well over 75,000 parents and caregivers cloth diaper their children through this website, her book, her YouTube Channel, and the Cloth Diapers for Beginners Facebook Group.