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?
* 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.
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.