How Moisturising Works: Humidity and Humectants

How Moisturising Works: Humidity and Humectants

What is the connection between air humidity, dry lips and frizzy hair? Can oils moisturise? Why is glycerin drying? Why do you need to add emollients to your DIY cosmetics? 

I got the answers from the article Humidity, Humectants and Hair. Do read that article for a detailed explanation and this post for the short-and-skinny, plus some practical tips.

How do cosmetics moisturise ?

Cosmetics don´t actually moisturise per se. They contain humectants that attract moisture from the surroundings and / or emollients and occlusives which seal in / seal out moisture.

What are humectants ?

They are the moisturising agents in hair and skin products. They are hygroscopic, which means they attract water and bind it to the skin. Eg: glycerin, honey, panthenol, propylene glycol, urea, lactic acid, sodium lactate, sodium hialuronate, aloe vera, hyaluronan.

*  What effect does dew point have on humectants ?

Humectants work best in a medium humidity (dew point between 1.5 - 10°C).
In low humidity conditions (dew point below 1.5°C) humectants will pull moisture from the skin and hair, since the air is very dry. This way they are drying. If you don´t want your skin & hair to dry out, apply moisturisers other than humectants. Don´t dry the hair completely after washing. Styling products with humectants should be applied only after a leave-in conditioner.
In high-humidity conditions (dew point above 15.5°C) humectants can attract too much moisture. Hello frizz ! Use products with emollients which smooth the hair scales, not allowing moisture to get in.

* What´s dew point ?

Humidity of the air is measured by dew point. Many weather websites, like Wunderground, show the dew point in your town over the day.

* What do emollients do ?

Emollients a name for several different substances, their common characteristic is that they form a film over the hair / skin, protecting if from drying out and forming a barrier against the environment. In high humidity conditions they prevent the hair & skin from taking in too much moisture. 
Oils and waxes are emollients. That´s how olive oil or jojoba oil "moisturise": they actually prevent moisture loss. I don´t recommend mineral oil (aka paraffin), which forms an impermeable layer that doesn´t let oxygen or moisture through. Ditto goes for coconut oil. Silicones are also good emollients, as long as you choose the water-soluble ones and not the stubborn ones that need harsh detergents to wash off.

* Tuning your cosmetics: 

Take a peek at the dew-point levels and consider adding emollients as well as humectants to your concoctions. For me that usually means a dash of Jojoba oil which I love for it´s lightness.

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