Summary
The hand sanitizer recipe is based on recommendations from the World Health Organization (WHO).
Introduction
Did you ever wonder what hand sanitizer is made of, or how you can efficiently disinfect your hands or other frequently touched surfaces like doorknobs? Handwashing is still the best way to keep your hands clean, but hand sanitizer is a great alternative for situations where clean water and soap are not available, and you can even use it to disinfect surfaces! Intrigued—try out making a hand sanitizer yourself!
Materials
- Measuring cups and spoons
- Pot to mix all ingredients
- Spoon
- Dishwashing soap
- Water
- Bleach (unscented)
- Funnel
- Isopropyl alcohol, with a concentration of 90% or higher
- Aloe Vera gel, available online at Amazon.com
- Clean bottle or tube to store the sanitizer, preferably with flip top.
- Optional: essential oil with a pleasant scent, available online at Amazon.com
- Isopropyl alcohol, with a concentration of 70% or higher
- Glycerol or glycerin, available online at Amazon.com
- Hydrogen peroxide, 3%
- Distilled water, available online at Amazon.com, or water that has been boiled for at least 1 minute (at sea-level) to 3 minutes (high altitude) and cooled to room temperature
- Clean spray bottle
- Optional: essential oil with a pleasant scent, available online at Amazon.com
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Prep Work
- Before you start, you need to disinfect all the tools you will use.
- Start by washing the tools in warm soapy water.
- Rinse with clean water.
- Make a disinfecting solution by mixing one tablespoon of bleach in one gallon of room temperature (not hot!) water. Bleach is a good disinfectant; it kills most germs.
- Dunk the tools in your sanitizing solution. For an extra safety measure, you can dunk the ingredient bottles too.
- Let the tools air-dry on a clean and disinfected drying rack.
- Wash your hands well just before you start the activity and disinfect your workspace.
Instructions
- This recipe is quick and easy and requires very few ingredients.
- Mix three parts isopropyl alcohol to one part aloe gel in a clean pot with a clean measuring spoon. For example, you can mix 1 cup of isopropyl alcohol with 1/3 cup of aloe gel, or 3 cups of isopropyl alcohol with 1 cup of aloe gel.
If you could have used isopropyl alcohol with a concentration of 100%, and your aloe gel didn't contain any alcohol, what alcohol concentration would this mixture have had? (Hint: first calculate the total amount of solution, then calculate what fraction of the total is alcohol, and finish by converting this fraction to a percentage. Answer: 3/4 or 75%) - If your isopropyl alcohol has a concentration 90% or higher, your solution will have a concentration of 68.5% or higher. The CDC (Center for Disease Control) states that hand sanitizers with an alcohol concentration below 60% are less effective at killing germs.
Is the alcohol concentration of your hand-sanitizer 60% or more?
- Optional: To give your sanitizer a more pleasing scent, you can add a few drops of essential oil.
- Pour the mixture into a clean bottle. Close the bottle well.
- Let your hand sanitizer sit for at least 3 days before using it.
Can you think of a reason why you would need to let it sit?
- When you start using the sanitizer, make sure to close the bottle after each use and avoid touching the mouth of the bottle when applying the sanitizer.
Why do you think you need to close the bottle after each use, and why should you avoid touching the mouth of the bottle of sanitizer with unsanitized hands?
- This recipe is easy to make but requires a few more ingredients.
- Pour 1 and 2/3 cups of isopropyl alcohol in a large clean pot. Remember to use clean utensils!
- Find the alcohol concentration on the bottle of isopropyl alcohol's label.
- If the isopropyl alcohol solution is ≥ 90%, mix in 1/4 cup of distilled or boiled and cooled water.
- If the isopropyl alcohol solution is < 90%, add another 1/4 cup of alcohol.
Can you think of a reason why the recipe calls for adding water when using a high concentration alcohol solution? Why do you think the water needs to be distilled or boiled and cooled?
- According to the CDC (Center for Decease Control), the concentration of alcohol in a hand sanitizer needs to be 60% or more.
If you could have used isopropyl alcohol with a concentration of 100%, can you calculate what the concentration of the alcohol would be in the solution you just made? (Hint: first calculate the total amount of solution, then calculate what fraction of the total is alcohol, and finish by converting this fraction to a percentage. Answer: 20/23 or 87%)
- For an alcohol concentration of 90% or more, your current mixture has an alcohol concentration of 78% or more, well above the 60% required.
- Mix in 1 tablespoon of hydrogen peroxide. This ingredient will inactivate bacterial spores.
- Use a clean spoon to pour a small amount of the current mixture on your hands. Rub it in.
What does it feel like?
- Use a clean teaspoon to add 2 teaspoons of glycerol to the mixture. When you are done, take a little of the glycerol on your hand and rub it on. (If glycerol or glycerin is not available, moisturize your hands after every use of the sanitizer.)
Does it feel different compared to the solution? What do you think is the purpose of glycerol in this recipe?
- Optional: To give your sanitizer a more pleasing scent, you can add a few drops of essential oil.
- Pour the mixture into a clean spray bottle. Close the bottle well.
- Let your hand sanitizer sit for at least 3 days before using it.
Can you think of a reason why you would need to let it sit?
- When you start using the sanitizer, avoid touching the nozzle when applying the sanitizer. If you need to touch it, wash your hands first.
Why should you avoid touching the spraying part of a bottle of hand sanitizer?
- To effectively sanitize your hands, spray it on, rub it around so every part of your hand gets disinfected, and let your hands air dry.
- To sanitize a surface with this spray: spray it on, let it sit a little and if needed, dry off. You can also use it to create disinfecting wipes.
What surfaces do you think might collect germs?
What Happened?
If you followed the directions, the concentration of your sanitizer is well within the requirements for alcohol-based sanitizers: an alcohol concentration above 60% and a 10 to 40% concentration of purified water. The alcohol helps kill germs, but water is needed to make the solution effective. Water makes it better at killing germs.
The alcohol solution probably felt cold on your hands because it uses the warmth of your hands to evaporate. It dries out the skin in the process. Glycerol (also called glycerin) is mainly added to keep your hands from drying out too quickly.
It is advised to let homemade sanitizer sit for three days before starting to use it so any harmful germs that accidentally made it into the hand sanitizer will be dead by the time you use the sanitizer. You need to close the bottle after each use for two reasons: it prevents the alcohol in the sanitizer from evaporating so the spray's potency will last longer, and it prevents airborne pathogens from entering the bottle. To keep the bottle clean and free of germs, you should not touch the mouth of the bottle or nozzle with unsanitized hands.
Frequently touched hard surfaces like doorknobs, elevator knobs, bathroom faucets, the remote control, phones and tables are often touched by a multiple of people. These are good surfaces to disinfect regularly.
Digging Deeper
There are some essential differences between hand washing and using a hand sanitizer. While washing hands with soap and water removes dirt, grease, and germs from your hands, hand sanitizer kills the germs on your hands. Because of that, it might surprise you that washing your hands frequently is still the best option for preventing being infected. It is even very efficient in fighting the spread of many diseases, including the common cold, the flu and COVID-19, the infectious disease caused by the SARS-CoV-2 coronavirus.
A germ is the collective name for many different types of microorganisms that can cause disease. Disease causing bacteria, viruses, fungi are all germs, and alcohol-based hand sanitizer with a large enough concentration of alcohol (according to the CDC, at least 60%) kills many of these. When left exposed to air, the alcohol concentration of hand sanitizer diminishes. When the concentration gets too low, the sanitizers may slow down the germs' growth and replication, but it will not kill them. Hand sanitizer also only works when it comes in contact with the germ, so you need to wash or rinse off all dirt that is stuck to your hands before using it for it to be effective. Handwashing, when done well, is still the best way of getting rid of germs.
To be effective at killing germs, an alcohol-based sanitizer needs to have an alcohol concentration above 60%. If you made your spray using a rubbing alcohol with a concentration of 90% or more, you added 1/4 cup of water to 1 and 2/3 cups of the alcohol solution for a total of 5/3 + 1/4 = 23/12 cups. 90% of 5/3 cups is 3/2 cups of alcohol in the final solution. 3/2 cups of alcohol in 23/12 cups of solution is 18/23 or 78%. The result is a mixture with a concentration of 78% or more alcohol. The remaining ingredients added less than two tablespoons to the mixture, too little to considerably change the concentration; it stays well above the 60% required for effective alcohol-based sanitizers.
If you made your spray using a rubbing alcohol with a concentration between 70% and 90%, you added less than two tablespoons of other ingredients to about two cups of the alcohol solution. As a result, the alcohol concentration stays well above 60%.
Water is essential in alcohol-based sanitizing as it slows down the evaporation rate. This increases the contact time of the solution with the germs, and thus makes it more likely to kill the germs. For bacteria and fungi, water also helps the alcohol to enter the germ cells. The recipes in this activity all make sure the sanitizer has a water concentration within the advised 10 to 40%
Some soaps are labeled antibacterial. You might wonder if these are better in fighting off diseases. While they kill some bacteria, they are not better than any other soap for fighting off viruses.
Ask an Expert
For Further Exploration
- See how effective you are at washing your hands with this fun hand washing activity.
- Give your hand sanitizer different smells by using different essential oils. Ask people which one they prefer, and why. Does one smell make them feel cleaner than another?
Related Resources
Project Ideas
Activities
Links
- CDC: Handwashing: Clean Hands Save Lives
- World Health Organization: WHO-recommended Handrub Formulations
