How germy is everyone's clean laundry?

Answer: Most people's clean laundry has germs UNLESS it was washed on a very hot cycle or chlorine bleach was used. A brand new pair of underwear out of the package has less germs than your underwear if you wash them on cold without bleach. 

Procedure

After I discovered that the dryer didn't kill all germs like I had thought and hoped, I wondered if everyone's "clean" laundry was actually full of bacteria. My family, neighbors, and friends were very good sports about me testing their laundry. I went to everyone's house when the dryer was done. Wearing gloves, I selected 2 pieces of laundry from their dryer. I put 1mL of sterile water on each piece of laundry.


Then I dabbed the laundry onto an agar plate. The plates were incubated in my warm incubator for 24-48 hours. 


About Agar Plates


For these experiments, I am growing bacteria on agar plates. Viruses can not grow on these agar plates. There are also some types of bacteria that won't grow on these agar plate. So, even if a plate looks clean, that does not mean that absolutely no microorganisms were present. However, the washing method that generates a clean looking plate most likely has less microorganisms total present than a washing method that generates a plate with lots of bacteria. In case you have never looked at an agar plate before, the white and yellow dots are colonies (or piles) of millions of bacteria. 

Results

Neighbor #1 an #2 had older top loader machines (not high efficiency). They both washed these 2 loads on hot with no bleach. #1 used All free and clear detergent.  #2 used Gain. As you can see, the clean laundry has a lot of bacteria. 


My neighbor Patty has a new HE Samsung front loader. Her load was washed on hot with no bleach and is still very germy. She used All Small and Mighty laundry detergent. My neighbor, Bethany, has a front loader and washed her laundry on hot with no bleach (she used vinegar and a Tide Pod). Bethany's laundry had a lot of germs. My laundry (Annie's laundry) and Courtney's laundry were both washed on hot with 1/2 cup chlorine bleach and looked pretty good. I used Tide Free and Clear detergent. Courtney has an older front loader and put the bleach into the dispenser. I have a high efficiency Samsung top loader, and I added the bleach to the wash water for this load in this particular experiment. 


My mother and sister Gina washed their laundry on hot with no bleach. Mom has an old top loader with agitator and used Tide. Gina has a high efficiency Samsung top loader and used original Tide liquid HE. Gina's looks surprisingly good for not using bleach. 


My sister Christy has an older top loader (not HE). She washed this laundry on hot and added the 1/2 cup chlorine bleach directly to the wash water and it was very, very clean. She measured the temperature of her wash water when the tank filled up using her meat thermometer and it was 130 degrees F. She used Sam's club detergent. 


My experiments show that most people have germs in their laundry. Since most of us survive just fine with germs in our clothing, I don't think we normally need to worry about it. I am in no way suggestion that everyone should bleach and ruin all of their good clothing. However, when someone in the house is sick with a stomach bug, or we are trying to get rid of a yeast infection or athletes foot, it would be helpful to know how to get our laundry as close to germ-free as possible. 

Do germs die in clean laundry over time? 

I imagine that some germs will die over time in clean dry fabric. I had my mother and sister mail me some of their laundry and it took 4-5 days to get here. There was still plenty of live bacteria in their laundry. 


I also put some of my clean laundry in a ziplock bag for a full week, and it still had plenty of live bacteria. So, some germs likely die over time but there is still plenty of bacteria alive after a week. 


Is ANYTHING germ-free?

We all know that the world is not a sterile place. There is lots of good and bad bacteria in and around us all the time. I am in no way suggesting that we need to kill all germs. But I did wonder if ANYTHING is really clean and free of bacteria. So, I tested a few things. I bought a new package of underwear from Walmart. 

I put 1mL of sterile water onto one pair. (Because bacteria transfer better to an agar plate when the fabric is wet.)

Then I dabbed that pair of underwear onto an agar plate. 

Nothing grew. Those new underwear were virtually free of bacteria. (Unless there was bacteria present that won't grow on this type of agar plate.)


I also tested some disposable Kleenex Hand Towels


I put 1mL of sterile water onto the hand towel and dabbed it onto the agar plate. 


Nothing grew.



I also tested some Bounty Paper Towel. 


Nothing grew. 

How to test your laundry for germs 


I wish I could test every single washing machine and every single detergent, but I just can't.  However, you can do a quick experiment with hydrogen peroxide to see how clean your laundry is. I made this YouTube video to show you how. You can repeat my experiments and test your own laundry. Just order these agar plates from Amazon and follow my steps. You don't really NEED an incubator. Just set the plates in a warm room for about 48 hours and see what grows. If you are repeating the experiments, it is important that you set the agar plates UPSIDE down to incubate. That means that the agar is on top and the lid is on the bottom. If you have questions, you can send me an e-mail and I'll talk you through it. phd.annie at gmail.com. This would also be a great Science Fair project for your kid! 

YouTube Video