Everyday Science: Why is Rubbing Alcohol Cold?

Whether it’s your arm rubbed down with an alcohol wipe before a shot at the doctor’s office, or a cotton ball of rubbing alcohol cleaning a scrape on your knee, it’s easy to notice that there’s something different about the way rubbing alcohol feels on your skin. Not only does the alcohol sting as it disinfects; it feels cold, even at room temperature.

Let’s explore that phenomenon and dive a little bit into the science of why rubbing alcohol feels cold on your skin. Like most things we talk about here at SGS Polymer Solutions Incorporated, there’s a clear and scientific answer.

Rubbing Alcohol — What is it?

Rubbing alcohol, is an alcoholic mixture that is made up of about 70% isopropyl alcohol. The remaining 30% includes water, denaturants, and perfume oils. It is known for its antiseptic properties and is often found in products such as hand sanitizer and disinfectants. Apart from its use in first-aid, it’s also used to kill infectious organisms and to prevent diseases from spreading in sterile areas like hospitals.

Rubbing alcohol is also commonly used as a cleaning agent. If you ever need to remove a sticky substance such as sap or gum from a surface, give it a try!

Rubbing alcohol also prevents swimmers’ ear! Its fast evaporation rate speeds up the evaporation of water in order to dry the ear and prevent infection.

So why does rubbing alcohol feel cold to the touch? Two words: evaporative cooling.

Evaporative Cooling

To explain this concept, we have to understand evaporation in general. Evaporation happens when a liquid becomes a gas. In order to evaporate, the hydrogen bonds holding the individual molecules together must be overcome in order for molecules to be released into the air. This process requires heat.

So what causes the cooling effect? Let’s use sweat as an example.

When you sweat, you’ve automatically begun the evaporation process; the hydrogen bonds are already breaking and absorbing thermal energy from your body. As the molecules evaporate, they remove heat from your body. This is heat transfer: thermal energy leaves your body, as the liquid becomes a gas. The result? A life-saving cooling effect, known as evaporative cooling, takes place, helping us maintain body temperature, and avoid overheating.

But what does this have to do with rubbing alcohol?

Alcohol evaporates much faster than water due to its lower boiling temperature. This allows more heat to be transferred faster, which makes it feel colder to the touch. To witness this “chilling science” in action, try this experiment!

From dry erase markers to dishwasher pods, we enjoy exploring the science behind everyday questions like this one. The same scientific principles that help us explain these parts of everyday life help us perform the complex independent testing that SGS Polymer Solutions Incorporated is known for.

We encourage you to stay curious and leave us your everyday questions in the comments below. We could end up blogging about it!