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Posted by Adria Marshall on

By definition, a humectant is a substance that adds or reduces the moisture level of the hair. Sounds simple enough, right? WRONG! Humectants are actually one of the most largely misunderstood ingredient types when it comes to hair care. This is because there is quite a complicated relationship between humectants and hair as it pertains to our environment. Want to learn more? Let's get started!

There are 5 categories of humectants:

  • Diols and Triols (e.g., Glycerin, Propylene glycol)
  • Hydrolyzed proteins (e.g., Keratin, Silk protein)
  • Esthers (e.g., PEG-x, Silicone Copolyols)
  • Sugars (e.g., Honey, Sorbitol).

Where it gets interesting is when attempting to grasp how these materials interact with the air. There are actually 4 scenarios that we need to consider to have a complete understanding of humectants.

Normal dew point conditions

When the dew point is... (Wait, what point? What is a dew point?) I'm so glad you asked! The dew point is the temperature in which water vapor begins to condense. Note: this is NOT the same as the humidity! Humidity is simply the amount of moisture in the air.

To calculate the dew point, you can:

1. Use this formula: Td = T - ((100 - RH)/5.) where Td is dew point temperature (in degrees Celsius), T is observed temperature (in degrees Celsius), and RH is relative humidity (in percent)

2. Go here (You're welcome)

So, as I was saying, when the dew point is 35 to 50 degrees F, it is considered normal, as far as our hair is concerned. There is just enough moisture in the air where the humectants in our hair can grab what they need to keep our hair bouncy and supple.

What to do? Not much - use product with a normal amount of humectants and keep it pushin'.


High dew point conditions

When the dew point is above 60 degrees F, it is considered high, as far as our hair is concerned. In these conditions, the humectants in our hair may attract too much moisture. This results in a swollen cuticle and hair that is frizzy and poofy. 

What to do? Ease up on the humectants for sure! You also might want to apply an oil or another anti-humectant to protect your hair shaft from over-absorption.


Low dew point conditions

When the dew point is under 30 degrees F, it is considered low, as far as hair is concerned. In these conditions, the humectants in your hair may actually pull the moisture from your hair into the environment. Wait? What?! Yes, This results in hair that is even drier than before the humectant was applied.

What to do? Again, lessen the amount of humectants that you're using and consider an oil or another anti-humectant to prevent moisture loss.


I hope that this blog help to demystify this subject a bit! What are your favorite humectants? How do you handle using them in various dew points? 



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  • Thank you so much! I have read so much about humectants and dew points in the past and gave up. THIS article gave me the “aha!” moment. It gets right to the point and I actually understand it now.

    Ella on
  • why do you use degrees Celsius in the calculation and for the effect on your hair Fahrenheit?
    you get a completely different number from the sum than the degrees you have outside. It’s a shame because I’ve been looking for this info for a while.

    Lonneke Verberne on
  • Duidelijk overzicht, dankjewel

    pieter on
  • This was very helpful and easy to understand.
    Thank you

    Beverly Bilbro on

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