It happens, you are in a pinch, the store is out of soap, your kid just touched the most disgusting thing ever or the cart at the grocery store — well don’t get us started there. Sometimes you need to use hand sanitizer when you can’t wash your hands immediately. But what happens when you can’t find it anywhere? With the recent COVID-19 outbreak, hand sanitizers are flying off the shelves – even the mini bottles that we usually all carry around.

Today we want to walk you through how to make your own, at home. This is a great lesson in math with chemistry! It also involves 99% rubbing alcohol so this is NOT an appropriate activity for children and adults should always handle the alcohol directly and safely.

CDC and Effective Hand Sanitizer

For Hand Sanitizer to be effective, the CDC is recommending we use of alcohol-based hand sanitizers with greater than 60% ethanol or 70% isopropanol.

What’s the difference between ethanol and isopropanol? Both are alcohol molecules with slightly different structures. Ethanol is the kind of alcohol that occurs naturally from fermentation, while isopropanol is made in a laboratory and tends to be what we find in say pharmacies or grocery stores in the first aid section. Rubbing Alcohol is the common name for Isopropanol.

What does it mean to be effective? Hand sanitizer is intended to kill germs, bacteria, and viruses. To do this, the alcohol needs to be strong enough. If it’s not strong enough, it won’t work. Strength in chemistry is measured in terms of concentration – so the percentages matter. We’ll show you how we calculate this below, but the CDC is saying that if you’re using a hand sanitizer with say 40% alcohol, well, that’s not really a hand sanitizer, so it’s better to call that say a hand lotion. Hand lotion is lovely! But it’s a different thing altogether from hand sanitizer and shouldn’t be used as a reliable way to kill germs, bacteria, or viruses.

Concentration, Dilution, and Math!

If you’re making a DIY hand sanitizer, it’s a good time to learn about concentration and dilution.

In chemistry, concentration refers to the amount of a substance in a defined space. So when we talk about rubbing alcohol, we see percentages listed that tell us how much alcohol is inside that container.

99% tells us that it’s 99% alcohol, with just 1% water. 70% tells us there’s 70% alcohol and 30% water.

We all know that when you add water to something it makes it less concentrated or strong, right? Well, that’s called dilution in chemistry. It’s the process of making something less strong, less concentrated.

When you mix let’s say 1 part of alcohol, with say 1 part water, the final mixture will have a lower concentration of alcohol.

You can figure this out with some math – we’ll show you an example below. The math is important to making a hand sanitizer that works!

Here’s math from our example:

3 parts rubbing alcohol (99% alcohol) + 1 part aloe vera (0% alcohol) = 4 parts (99% * 3/4) or approximately 74% alcohol

What if we add in a few drops of essential oils? Well, essential oils can vary, and not all drops are the same size, and most people don’t have a way to measure exactly how many milliliters are in 10 drops. We play it safe here by using only 3-4 drops and mix it into your aloe vera first, and then measure out 1/4 cup exactly of your aloe vera/essential oil mixture.

Supplies

3-4 drops Tea Tree Oil or other Essential Oil, optional

3/4c of 99% Rubbing Alcohol (Isopropanol)

1/4c Aloe Vera Gel

Some accurate kitchen measuring tools!

Container – We used a few small travel ones!

Instructions

Take your Aloe Vera and your essential oil drops if you’re using them into a bowl. Mix. Carefully measure out 1/4 cup.

Place the 1/4 cul into a bowl (we recommend one with a spout so you can pour it later). Mix in 3/4 cup of your 99% rubbing alcohol solution. Pour into your bottle for use!

Squeeze a dime sized dollop of gel into your hands and rub together. Use as often as needed.