A: 3 methods of moisturization.
Purpose: To reduce how much water evaporates through your skin. (Cosmetic scientists refer to this as TransEpidermal Moisture Loss or TEWL.) Occlusive agents form a hydrophobic barrier on your skin that keeps the water on the inside. The most effective examples include petrolatum, mineral oil, and dimethicone. Some plant oils help occlude the skin but typically they are included more for their emolliency.
Purpose: In this context I’m talking about adding water to skin and the only ingredient that can really do that is…water. For some product types (like shampoo) water is just a carrier or solvent for other ingredients. But in the case of moisturizing lotions the water contained in the product is also hydrating your skin.
Purpose: To bind (or even attract) moisture to your skin.
Ingredients known as “polyols” have the ability to hold on to large amounts of water and keep it close to your skin. In some cases they can even absorb moisture from the atmosphere. These ingredients have two drawbacks: they can make your skin feel sticky and when the air is REALLY dry they can actually pull water out of your skin instead of the atmosphere. Examples include glycerin, sorbitol, and hyaluronic acid. Glycerin and sorbitol work pretty well and they’re cheap. Hyaluronic acid can hold hundreds of times its weight in water but it’s really expensive.
What does it mean to be “plant-based”
For example, if the “lauryl” part of a surfactant like sodium lauryl sulfate is made from coconut oil, does that mean that SLS is a natural, plant-based ingredient?
Are plant-based ingredients good moisturizers?
We found an “occlusivity rating” of various oils that compares plant-based moisturizers with petrolatum and mineral oil. In this evaluation a higher scorer is better so clearly petrolatum and mineral oil are the best. But plant oils (like olive oil, rice bran oil, and shea butter) do a pretty good job as well.
Mineral oil 75+
Olive oil 70
Rice bran 70
Shea butter 70
Macadamia oil 70
Castor oil 68
Soybean oil 68
What about other ingredients?
To determine if a product is plant-based you need to look at more than just the moisturizing ingredients. You have to evaluate the emulsifiers, thickeners, pH control agents, and so on. So pick one of your favorite “natural” brands, preferably one that lists the sources of their ingredients in parenthesis. For example, Seventh Generation puts an “*” next to each plant derived ingredient. Some examples:
cetyl hydroxyethylcellulose (plant-based),
essential oils and botanical extracts*
The Beauty Brains bottom line
The best plant based moisturizing ingredients are olive oil, rice bran oil and shea butter. Look for a natural brand that you trust that discloses the source of their ingredients and then look for these as the first few ingredients.