As I Iearn more about the ingredients in my beauty products, I am shocked by how often companies interchangeably (and incorrectly) use the words “hydrating” and “moisturizing.” And, truth be told, I’ve only recently understood the distinction myself. The difference between hydration and moisture for hair and skin boils down to this:
hydration is the process by which water enters the hair or skin
moisturization is the process by which that water is locked in so it does not escape the hair or skin
therefore, when it comes to topical care, we usually hydrate first and moisturize second
Isn’t science awesome? While hair and skin behave differently, the principles of hydration and moisture similarly apply to both. By understanding these principles and their distinction, you will be well on your way to improving the overall health and appearance of your two greatest assets.
As a disclaimer, I am not a dermatologist, scientist, esthetician, or haircare professional. All opinions on this topic are my own based on research and discussions with hair stylists and estheticians over the years.
Let’s start with hydration. Hydration is where it gets a bit complicated because hair and skin absorb water differently.
Hydration for Skin
“Dehydrated” skin is essentially skin that lacks sufficient water. We can “hydrate” our skin in a number of ways. Drinking water is the primary way to do this and a complete non-negotiable when it comes to skin hydration. This is because unlike the hair cuticle (discussed further below), the outer membrane of our skin, the epidermis, is largely impermeable. Thus, you simply cannot adequately hydrate the skin by showering or bathing. Sorry, guys.
However, the skin can absorb a certain amount of substances through topical application. Humectants, for example, or substances that attract water to your skin) like glycerin, hyaluronic acid, honey and aloe vera. For skin, hyaluronic acid is said to be the best hydrator as it reportedly can attract and bind to the skin up to 1000x its weight in water! So, when you are determining whether a product is hydrating for the skin, look for humectants high up in the ingredient list. I also exfoliate regularly so that when I hydrate externally, I can slough off any dead skin cells so that they won’t hinder the absorption of humectants.
Note: the trouble with humectants, however, is that they attract atmospheric water; so if the air is dry, using too many humectants can cause the skin the skin to feel dry. This principle is discussed further below in re: hydration for hair.
Hydration for Hair
Though the concept of hydration is similar for hair, an important distinction is that, unlike the outer layer of the skin, the outermost layer (or cuticle) of the hair is permeable. Thus, water can penetrate the hair through the cuticle. The cuticle is formed by dead cells that overlap, like roof shingles or scales on a fish, and serve to protect the hair. In order for water to enter the hair shaft, it has to get through that cuticle.
Thus, while drinking sufficient water is also crucial to hair hydration because of the relationship that the hair follicle has with your skin, all hair types benefit from external hydration. We can externally hydrate by using conditioners rich with water and humectants (e.g., glycerin, aloe vera, etc.) and by applying these conditioners via squish to condish or with heat so that your cuticles can open up to absorb the product. While most conditioners also contain oils and ingredients that moisturize (see below), their water and humectant content signal whether they are hydrating, too.
However, remember that the cuticle also permits water to move both ways. This is especially important to watch out for if you use humectants, as they draw in whatever moisture is in the air. So, on a muggy or high dew point day, humectants can draw too much moisture from the air into the hair. Conversely, on a dry or low dew point day, humectants will cause your hair to feel dry and mimic the air around it.
Regardless of your hair or skin type, moisturizing is a critical step in your routine. When we “moisturize” we are trapping that essential water so it doesn’t exit the skin or hair. Remember those humectants and how they just as easily can cause water to escape the hair or skin? It follows, then, that for your topical hair or skincare regimen, hydration comes first and moisturizing follows to help keep that water where it is most needed. Typically, we moisturize most effectively with natural or plant-based oils and products that contain these types of oils (so, no mineral oils). Natural oils are crucial, as they are similar to the naturally-occurring oily substance called sebum present in both hair and skin.
Moisture for Skin
For skin, we can moisturize with pure, natural oils to seal in water and prevent water and moisture loss throughout the day. Additionally, oils mimic skin’s sebum. Sebum works to protect, lubricate and nourish our skin. It prevents it from drying out and prematurely aging. Those with “oily skin” might have an overproduction of sebum, while those with “dry skin” may lack it. It is said that even for “oily skin,” using natural oils will signal the skin to stop overproducing sebum, thereby providing essential moisture without added oiliness.
Note: there are dissenting opinions on whether one should use an oil before a cream for skin. I have found that applying oils after creams works best for me, but figure out what works best for you!
Moisture for Hair
For hair, oil is a wonderful moisturizer for similar reasons. Just as it is for the skin, sebum is essential for hair health. Sebum is produced on the scalp. It then passes through the hair follicle and travels down the hair shaft, acting as a natural conditioner to soften and protect the hair. As with the skin, using natural oils on your hair mimics sebum. At the same time, oils seal in water so it does not escape through the cuticle. A practical example of this in curly hair care is the LOC (leave-in, oil, cream) method, which calls for oil to lock in moisture after hydrating with a leave-in conditioner. In addition to oils, butters (e.g., shea butter) moisturize the hair, too.
Wait…say that again?
Just remember that the hydrating product comes first, as it infuses the hair and skin with the water it needs. Hydrating products should be comprised of humectants; for hair products in particular, also look for water high up in the ingredient list. Moisturizing products should contain natural oils and be used after the hydration in order to seal in that water. Moisturizing products also help mimic the wonderful sebum that hair and skin lose over time. Finally, read ingredients carefully (as opposed to relying on product claims) to determine if the product is truly hydrating or moisturizing, or both.
If you found this helpful or have any alternate views, please let me know in the comments.