After I did a bunch of laundry experiments (which you can see here), I had many requests to determine if hanging laundry out in the sun would kill germs. To do this, I took all my dirty kitchen towels and washcloths which had been sitting in a laundry basket for a few days and numbered 7 of the washcloths with permanent marker (1 through 7). Then I washed the washcloths with the rest of the kitchen stuff on cold in my Samsung high efficiency top loader. I do not recommend this machine. Look how little water it used for these cloths. They were barely agitating. What you see here is really germ soup. I used Tide free and clear detergent. I did not use bleach. After the 53 minute wash cycle, I dabbed each "clean" washcloths onto its own agar plate (which bacteria love to grow on). You can purchase some of these agar plates for your own experiments here on amazon Then I put cloths numbered 1 and 2 in my Samsung HE dryer on the sanitize setting for 1.5 hours with the rest of the kitchen laundry. I do like this dryer pretty well. I hung cloths numbered 3 and 4 up to dry in my computer room for 4 hours. Please ignore how messy this room is. I hung cloths numbered 5, 6, and 7 outside on a hot sunny day (88 degrees F) for 4 hours (from 2pm to 6pm). There was hardly a cloud in the sky. Halfway through the drying, I moved the clothes line so the opposite side of the cloths was directly facing the sun. So, both sides of the cloths had time in the sun. I did notice that some bugs landed on the cloths which could bring more bacteria to them. After the specified time, I blotted each cloth onto another agar plate. I wet the cloths with a little sterile water before I blotted them onto the agar plates because the germs transfer better when they are damp. Then I incubated the cloths for 24 hours in my warm incubator (about 90 degrees F). As you can see, the washcloths were disgustingly FILTHY and full of bacteria after going through the washing machine. Yuck. The sanitize setting on the dryer killed most of the bacteria. In case you don't know what you are looking at, each white or yellowish dot is a colony (or pile) of millions of bacteria. The cloths that hung up to dry in the computer room were still disgustingly filthy after hanging up to dry inside for 4 hours. The cloths that were hung outside in the sun were much cleaner than the ones that hung up inside. Maybe not quite as clean as the cloths that went through the dryer, though. Just as I had hoped, hanging cloths out to dry on a sunny day killed the majority of the bacteria! It certainly could be possible that bugs that landed on the cloths and dirt blowing in the breeze could have added a little bacteria to the cloths as well. So, if you like to hang your laundry out to dry in the sun, go for it! It really reduces the germs! Does the sunlight kill germs on hard surfaces?I put 1mL of this germ water onto each plate and rubbed it around with my gloved hand. Then I let the plates dry completely inside the house which took about 2 hours. Once the plates were dry, I stacked them up. The "sun" plate was on top and the "dark" plate was on the bottom. Then I took the plates outside on a completely sunny blue sky day. It was about 80 degrees F. I set the plates on my patio table on top of white paper towel, because I didn't want the plates to get too hot. I covered the edges with white towels because I didn't want sunlight sneaking into the cracks between the plates. The reason that I stacked the plates as opposed to keeping the "dark" plate inside the house was because I wanted the plates to be at the same temperature. After 4 hours of sitting out in the sun, I used a sterile swab (wet with sterile water) to rub each plate and then rubbed the swab onto an agar plate. The agar plates were incubated for 24 hours in my warm incubator (about 90 degrees F). As you can see, there is a significant decrease in the amount of bacteria on the plate that was exposed to the sun. I repeated the experiment a second sunny day and got the same results. Sunlight Conclusions |