Purell Surface Disinfectant and Citrus II Independent Testing

How well does Purell Surface and Citrus II kill germs?

Answer: Purell Surface kills some germs and is safe to use on more surface types than bleach or hydrogen peroxide.


To test these products, I did the same countertop experiments that I usually do. I sectioned off squares on my countertop using masking tape. I made "germ water" using dirt from the backyard and water. I filtered it through a paper towel to remove chunks. Then I scraped colonies of bacteria from a previous days agar plate and mixed that in. The previous days plate was a "dirty sink" plate. So, there was lots of dirt and lots of bacteria in these experiments. I put 1mL of germ water onto each square. 

I used a gloved finger to spread the germ water around the square. Then I let the squares dry completely which took about 2 hours. If you would like to see pictures of every step in this process, please scroll to the top of this mile-long page. I go into greater detail about my experimental procedure up there. 

After the squares were dry, I put .5mL of each product onto its respective square. I spread the product completely around the square using a clean gloved finger. For the dirty positive control, I just put water on the square. For the clean negative control (which didn't have any germ water on it), I just put sterile water onto the square. I set timers and let the product sit on the square for 5 minutes. 

After 5 minutes, I swabbed the square and rubbed the swab all over a clean agar plate. 

The plates were incubated for 48 hours in my warm incubator (about 90 degrees F). 

Understanding Agar Plates

In case you are new at looking at agar plates, let me explain. Agar is a Jello-like substance that bacteria and fungus like to grow on. The whitish/yellowish dots you see are colonies (or piles) of millions of bacteria. Some types of bacteria are not able to grow on these agar plates. Viruses can not grow on these agar plates. So, just because a plate looks clean, doesn't mean that no microorganisms whatsoever were present. We assume that a clean plate means that most bacteria were killed. However, there is the tiny possibility that the cleaning product just stopped the bacteria from growing as opposed to actually killing it. Also, I can't make any determination as to the time it took the product to kill the bacteria since the product was still with the bacteria on the agar plate. (Both the bacteria and the cleaner would be picked up in the sterile swab.) So, I don't know if it took 1 minute to kill the bacteria or hours. These experiments are still very useful when used to compare cleaning products and cleaning methods. 


In these experiments, I'm comparing everything to 3% hydrogen peroxide which always works really well. Most cleaning products do not do well in these experiments because they can't handle so much dirt and germs. It is surprising how many products are supposed to be used on already clean surfaces. Some products that don't do well in these experiments, might still do a good enough job on your only slightly germy countertop. 

Citrus II seemed to do a little better than Purell Surface. Purell Surface is a product advertised to be safe for food contact surface and its active ingredient is ethanol. I've learned from my experiments that most alcohol products don't do well in the presence of actual dirt. So, Purell Surface might be fine on relatively clean kitchen countertops. I will be testing it in the sink experiment. 

Sink Experiments

Many cleaning products are not strong enough to do well in my countertop experiments with dirt and lots of germs. So, I also like to test everything in a real life situation, the kitchen sink. Any cleaner that we expect to kill germs, should be able to kill germs in my kitchen sink experiments. To do these experiments, I use my neighbors' kitchen sinks. They don't disinfect their sinks very often so they are usually germy enough for me to do a good experiment. I can only do one experiment per week per kitchen sink because there needs to be time for plenty of bacteria to grow again. So, these experiments take some time. I have not done all of the products yet. Check back for more results. 

First I rinse off the sinks so there is no food debris stuck on them. Then I swab both sides of the dirty sink and rub the swabs onto agar plates. Then I spray the product all over one side of the sink. I usually use at least 20 sprays to fully cover that side of the sink. The other side is the control and I spray that side with 3% hydrogen peroxide because that always seems to generate very clean results.

Purell Surface in the sink

For these experiments, I used 25 sprays of Purell Surface disinfectant on one side of the sink and 25 sprays of 3% hydrogen peroxide on the other side of the sink. I let them sit for 5 minutes and then swabbed. 

As you can see, the Purell Surface worked well, but did not kill quite as much bacteria as the 3% hydrogen peroxide. Since it didn't do well at all in my countertop experiments with dirt, we know that Purell Surface is a product that only works on a pretty clean surface. The instructions also say that it needs to be used on a clean surface. Purell Surface is advertised to kill the norovirus surrogate in 30 seconds which is great. However, we can tell that it will only kill that norovirus if the surface is already super clean. Purell Surface is mostly ethanol and makes me cough a lot using it. Disclaimer: I can't be 100% certain that any product that I test is actually killing bacteria as opposed to somehow preventing the bacteria from growing on the agar plate by some other means. I also can't tell how long it takes a product to kill the germs since the product is picked up in the swab with the germs and stays on the agar plate during incubation. 

If you would like to suggest an experiment, please post on my facebook page. I also really need to earn money from this website in order to keep doing experiments (agar plates, essential oils, and cleaning products are expensive). If you want to contribute, please use my Amazon affiliate links. Just click on any of my links that go to amazon, and buy whatever you want. You don't have to buy what I recommend or even the product that the link goes to. Here is a link. I'll get a small percentage of the sale and use the money to buy experiment supplies. Thank you.

--Annie Pryor, Ph.D.