Can you test heat protectants with fire? The Science

You might’ve seen videos of people testing their heat protectant products by trying to light them on fire. As many of you may have suspected, this is a really ineffective test for whether a product protects your hair from heat.

Where does this test come from?

This test seems to be promoted by a lot of people selling Monat, an MLM haircare brand. 

To do the test, you dip a cotton bud (Q-tip) into the heat protectant, then light it with a lighter. According to the videos, if it won’t light on fire, it’s a good heat protectant. But that’s not how heat protectants work.

How do heat protectants work?

Heat protectants work by forming a film on hair that spreads out heat evenly. It’s like using a frying pan versus cooking directly on a fire – the extra layer spreads heat spreads more evenly.

This means you won’t end up with hot spots where your hair starts decomposing while other parts of your hair are still too cold, and not being styled.

Related Post: How do heat protectant hair products work?

What’s really happening in the test?

Fire and heat are different, chemically. Heat is molecular-level vibrations, while fire is combustion: something is reacting with oxygen and burning.

Cotton, for example, is used in oven mitts. It’s really good at protecting your hands from heat, but it’s going to burn if you light it on fire, because heat protection and combustibility are two completely different properties of substances.

Most of the time, these tests are actually showing which products contain water. Most heat protectants contain some combustible ingredients dissolved or suspended in a solvent. If the solvent is water, the product tends not to combust, but if the solvent is oil or alcohol (both are also very combustible). 

Is this a good test?

Ironically, products that do light on fire might be better at protecting your hair during heat styling.

Too much water is actually bad in heat protectants, because water can absorb into hair and boil. It doesn’t evaporate as easily as alcohol, but it boils a lot more easily than oil. So when you apply heat to hair, the water inside can boil explosively, much like popcorn – this causes “bubble hair”.

Related Post: My Top (Mostly Cheap or Free) Haircare Hacks

I also debunked this test and a lot of other haircare misinformation on social media (sulfates, silicones, benzene etc.) in a video, if you prefer watching or listening!