A Moisturizing, Hydrating Adventure: Second Edition
occlusives, emollients, emulsions, oh my!
Hello hello, nice to see you all again.
Tomorrow morning you’ll be getting a Hotline Skin special edition and in advance of that, I wanted to refresh a post from a few years ago. When I went to find said post, I discovered that I coincidentally published it nearly 3 years ago to the day, on February 20th, 2022. What’s more, that happens to be the day I got engaged! Just a few hours after it hit your inboxes. Anyway, my point is that reading Hotline Skin this week may bring you good luck and you should forward to a friend to really lock that luck in.
A Moisturizing, Hydrating Adventure
Originally published 2/20/2022, revised 2/2025
The original question:
I recently read this and am now afraid I am doing skin all wrong. I have been using Indie Lee’s Squalane Oil as my “moisturizer” and am now finding out it…doesn’t moisturize? Should I quit life? Or just buy a different moisturizer? I have dry and sensitive old crone skin.
The article opens by talking about words in the beauty-industry that have actual, scientific meanings, but aren’t always used correctly, specifically hydration and moisture.
They’re almost always used interchangeably and understandably so–they go hand-in-hand and contribute to similar processes in our skin. But scientifically they have very clear, distinct meanings. Moisture refers to oil and hydration refers to water. Your skin relies on both water and oil to function and thrive. So how does that translate into what we put on our skin and whether squalane oil can be your moisturizer?
Your skin barrier is composed of dead skin cells and oil-based things like lipids, ceramides and fatty-acids. Oil, by definition, is devoid of water, so it cannot possibly hydrate. But oils help to reinforce the skin barrier, making it harder for water to evaporate. Water is constantly evaporating from the surface of your skin, via a process called transepidermal water loss or TEWL. Water keeps your skin plump by swelling your skin cells, reducing the appearance of fine lines and wrinkles and improving elasticity. Acne-prone skin is often dehydrated because people are hesitant to use anything with oil, which makes it easier for water to evaporate. But not all oils are comedogenic.
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I came up with a theory to explain why there’s so much confusion around these terms. It’s because moisture, or moisturization, can refer to one of three things: product category, ingredient category or process.
The process of moisturizing refers to replenishing and strengthening your skin barrier, the outermost layer of your skin. This process is inherently related to hydration (which literally means the addition of water) since water is necessary for barrier function.
There are 3 categories of moisturizing ingredients that enable this process:
Occlusives (thicker oils/waxy balms that create a barrier on the surface of your skin to prevent water from evaporating, such as petroleum jelly, dimethicone and shea butter)
Emollients (oils that smooth, soften and fill in gaps, such as plant oils, ceramides, silicones and squalane. Some emollients, like shea butter, are also occlusives)
Humectants (molecules that attract and retain water to prevent evaporation, such as hyaluronic acid, glycerin, urea and panthenol)
The cream or lotion product that you put on at the end of your routine is called a moisturizer. Moisturizers are a mix of emollients, occlusives and humectants. They also contain water. The humectants in the formula help hold onto the water, while the emollients/occlusives help smooth the surface and prevent the water from evaporating.
All skin, from the oiliest to the driest to the most acne-prone, needs a balance of water and oil to function, but the ratio & types of occlusives/emollients/humectants to achieve this balance differs for everyone based on skin type and preference. Facial oils are a distinct category from moisturizers because they do not have any water. For some people, especially with drier skin, facial oils are a great addition to moisturizer to create an extra occlusive barrier or help soften rough skin. As I advised to the person who submitted the original question, your “dry, sensitive, old-crone skin” just needs some hydration! Grab a moisturizer (the product) and add a few drops of your squalane oil on top or mixed in.
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When it comes to picking a moisturizer, there’s another consideration beyond the types of occlusives, emollients and humectants, which is how they are combined. As you know, oil and water, famously, don’t mix. In chemistry, we call them immiscible substances. An emulsion is the mixture of two immiscible substances (ex: oil and water) kept together by an emulsifier. There are many different types of emulsifiers. Almost all of your products are emulsions because otherwise the oil and water would separate.
Oil-in-water emulsions are the most popular. As the name implies, oil droplets are dispersed in water. They’re easier to formulate and tend to feel lighter since there is more water. The can range from gel-creams to lotions in consistency and are easy to rub in.
Water-in-oil emulsions are known as reverse emulsions. In these formulas, water droplets are dispersed in an oily substance. They are more difficult to formulate but allow for a lot of variability since there are many options for the oil-component. Since they are oil forward, reverse emulsions have a unique consistency, that’s more tacky and rich. They take a bit longer to rub in, but leave a nice glow and provide long-lasting occlusive benefits. Classic cold cream is the original reverse emulsion. Three super popular products you may not have known are reverse emulsions include Augustinus Bader’s The Rich Cream, U Beauty’s Super Hydrator and InnBeauty Project’s Extreme Cream. Historically, I haven’t been a fan of reverse emulsions. Emphasis on historically. We’ll pick up back here tomorrow.
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xx,
Jolie
Great piece! You did a great job of braking the science down into easy to understand bites.
The question got me. 💀