Do germs die in the washer and dryer?


Answer: Not all of them. Lots of germs survive a trip through the washer and dryer unless you use a very hot cycle or chlorine bleach. Here are my experiments to prove it. 

Procedure


To do these experiments, I blotted 10 pieces of dirty laundry on an agar plate.  


Then I washed the laundry on a specific cycle. I used either my Whirlpool duet HE front loader or my Speed Queen top loader. 


I used full/large loads of laundry.


For most of these experiments I used 1/2 cup of Kirkland Free and Clear laundry detergent unless I specified that I used something else. (I have tested lots of other detergents and laundry products on this page.)


After washing, I blotted 10 pieces of laundry on another agar plate.


Then I dried the laundry on an either normal cycle or sanitize cycle in my Whirlpool dryer.


After the dryer, I blotted 10 more pieces of the clean, dry laundry onto another agar plate. I got the pieces of laundry slightly damp with clean tap water before blotting because germs don't transfer well from a perfectly dry cloth onto an agar plate. I tested the tap water for germs, and it was always clean. 


The agar plates were incubated for 24 hours in my 90 degrees F incubator. Then I photographed them.

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


White load (socks, underwear, towels) washed in a normal hot cycle in my Whirlpool duet HE washer (51 minute cycle) with 1/2 cup of Kirkland Free and Clear detergent.and dried on a normal cycle in the dryer 

White load (socks, underwear, towels) washed on sanitize cycle with heavy soil, extra rinse, and steam boost in my Whirlpool duet HE washer (a 2 hour and 15 minute cycle) with 1/2 cup Kirkland Free and Clear detergent and dried on a sanitize cycle in my dryer.



White load (socks, underwear, towels) washed on that same 2 hour and 15 minute sanitize cycle with heavy soil, extra rinse, and steam boost in my Whirlpool duet HE washer with 1/2 cup Kirkland Free and clear detergent AND 1/2 cup chlorine bleach (put in the dispenser) and dried on a sanitize cycle in my dryer. 

A cold load (jeans, shirts, outerwear) washed on a cold load in my HE Whirlpool duet washer with 1/2 cup Kirkland Free and Clear detergent and dried on a normal cycle in my dryer. 

A hot, heavy soil cycle in my Speed Queen top loader (not HE, fills all the way up with water, 33 minute cycle) with 1/2 cup Kirkland Free and Clear detergent and a sanitize cycle in my Whirlpool dryer. 
The Speed Queen only gets as hot as the tap water filling it up. My full washer is usually about 130 degrees F. I've noticed that when it is only 120 degrees F it doesn't kill germs nearly as well. I may need to crank up my hot water tank and then see how clean the Speed Queen can get the laundry. 
 
If you don't have a meat thermometer yet, please get one.


A hot, heavy soil load (underwear, socks, washcloths, towels) in my Speed Queen with 1/2 cup Kirkland Free and Clear detergent AND 1/2 cup chlorine bleach. Dried on the sanitize cycle in my Whirlpool dryer.


Cold dark load (jeans, shirts, outwear) in Speed Queen with 1/2 cup Kirkland Free and Clear detergent and dried on a normal cycle in my dryer.

To really test the power of the dryer sanitize cycle, I washed a white load (which is germier than a dark load at my house) on cold in the Speed Queen. I used 1/2 cup Kirkland Free and Clear detergent. Then I dried it on the sanitize cycle. 

Conclusions


My results show that there is still a lot of germs in clean laundry unless it is washed in hot water (130 degrees F or greater) or chlorine bleach is used. The hot cycle on the Speed Queen top loader did as well or better than the sanitize cycle on the Whirlpool duet, but its effectiveness is totally dependent on the temperature of your hot water coming from your pipes. The dryer kills the majority of the germs but not all. I also learned that dry clothing is not nearly as germy as wet laundry (that has been sitting around). So, it is a good idea to use one laundry basket for good clothes that you are going to wash on cold such as jeans and shirts (so they stay dry and don't grow so much bacteria). Use a second basket for underwear, wet towels, and washcloths that you can wash on a sanitize cycle. I don't think it is important to worry about all the germs in your clothing unless it has been contaminated with a stomach bug or you have some sort of infection. Having really clean underwear can help prevent feminine infections. Clean socks can help those trying to get rid of athletes foot. I have done many experiments testing different detergents, please see this page for those results. Please use my Amazon affiliate links, like this one, when you shop on Amazon so I can earn some money to pay for my experiments. Thank you. 

How much bacteria is in the washer and dryer themselves?

I guess it is easy to imagine that if the laundry comes out of the washer full of germs, there are probably a lot of germs in the washer itself. I swabbed the walls of the washer after a cold dark load and there was plenty of bacteria. So, when someone has a stomach bug and you wash vomit covered laundry without bleach, there are still very likely to be viruses in the clean laundry AND contaminating the washing machine. 



The dryer walls get so hot that I find it hard to believe that any germs could live in there. I swabbed it and there were just a few colonies. The dryer is generally much cleaner than the washer, though. 


Here I swabbed my  HE Whirlpool Duet front loader washer AFTER the self-clean cycle. I used 1/2 cup chlorine bleach in the dispenser during the self-clean cycle. 


The self-clean cycle worked great, and I'm going to remember to do that once every few weeks and ALWAYS after washing stomach flu laundry. 





Older Experiments


I have been doing laundry experiments for years. Here are some of the original experiments that I did to determine if germs died in the dryer.

Does the dryer kill germs?

I have always assumed that a half hour in a hot dryer would kill most germs. I've been known to throw an article of clothing in the dryer that I didn't want to wash just to kill germs. However, I knew I needed to really test it to be sure that most germs die in the dryer. First I drew circles on dishcloths.


Then I put 1mL of dirty "germ water" on each circle. I made the germ water by mixing a little scoop of dirt from my back yard in water and filtering it through paper towel to remove chunks. 




I pressed one circle from each cloth onto an agar plate. This would be the dirty positive control. I also pressed a clean spot on the cloth that had no germ water onto an agar plate to be the clean negative control. 

Then I put the cloths in my Samsung Dryer on the "Sanitize" setting for 30 minutes. 


After the cloths were done in the dryer, I added 1mL of sterile water to each dirty circle, and pressed those circles onto agar plates. (Bacteria don't transfer well from a cloth onto an agar plate unless the cloths are wet.) The agar plates were incubated for 24 hours in my warm incubator (which is about 90 degrees F). I have a picture of the incubator on a few of my other experimental pages if you want to see it. 



Much to my surprise, there really didn't seem to be a decrease in the amount of bacteria on the plates after the 30 minutes in the dryer or 1 hour in the dryer. 

I repeated the experiment again using a VERY germy cloth. This time I put it in the dryer for 2 hours, and I did see a significant decrease in the amount of bacteria. 



So, it appears that the dryer does not kill all germs like I had hoped. It can kill the majority of germs, though, IF you have it on a very hot setting. I noticed that my high efficiency dryer doesn't always get that HOT when I only have one or a few items in it. Some of the high efficiency dryers like mine sense how wet a load is and will only use the minimum amount of heat necessary. So, my dryer only gets HOT when there is a normal sized WET load in there. Even if I put it on the "sanitize" setting, it doesn't seem to get that hot if I only have a few things in it. I also attempted to take the temperature of my hot laundry. I opened the dryer door in the middle of the cycle, stuck my meat thermometer in there, and pressed the clothes tightly around it. The hottest that I ever caught my dryer was 160 degrees F. I really would have thought that temperature would have killed more germs than it did.