You probably had to have shots before. You probably remember the cold feeling you had when they wiped your arm clean right before they put the needle in.
Have you ever wondered why your arm feels cold when they disinfect it? Well, it’s a very simple natural process called ‘evaporative cooling’. It’s the same process that explains why we sweat.
Imagine a hot summer day, it’s 30 °C outside, the sun is burning, sweat is forming on your forehead: the evaporative cooling has started. Now what is evaporative cooling exactly? Let us first explain evaporating. We all know water evaporates. The evaporating, going from a liquid to gas, happens because gases have a higher energy level. This means that molecules would rather be in the gas phase than in the liquid phase. When the liquid is water, evaporating means breaking the hydrogen bonds that are present in the liquid form. The breaking of the bond (one of the strongest bonds) requires energy or heat. This means while we sweat, heat is taken from our body and our body cools down and overheating is prevented. This explains why it’s called ‘evaporative cooling’.
The same thing happens with rubbing alcohol. Rubbing alcohol is a mixture that contains mostly isopropyl alcohol, but also water, denaturants and perfume oils. It is derived from crude oil and processed until it can be used as a disinfectant. It removes germs (but not all of them) and is therefore also used in hand sanitizers.
As rubbing alcohol exist mostly of isopropyl alcohol, it contains the same characteristics. Therefore it has a much lower boiling point than water (about 82 °C). Thus it starts to evaporate at a much lower temperature, such as room temperature. The lower boiling point also has an effect on the speed of the evaporating, making it much quicker.
So the next time it’s a hot summer day or when it’s time for your flu shot, you’ll know exactly why you’re sweating or why your arm feels cold!
Sources:
https://www.polymersolutions.com/blog/rubbing-alcohol/
https://www.reference.com/science/rubbing-alcohol-feel-cold-1c933d7d14cfc689
https://health.answers.com/mobile/Q/Why_does_your_skin_get_cold_when_it_comes_in_contact_with_rubbing_alcohol
http_www.wikihow.comimages33aUse-Rubbing-Alcohol-Step-3
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