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Moisturizing vs Hydrating? What's the Difference?

Updated: May 19



HOW OUR SKIN IS HYDRATED


Hydration relates to the water content of the uppermost layer of the epidermis – the stratum corneum. In effect, our skin forms a water gradient from the bottom of the epidermis to this outer, protective layer that is in contact with the external environment. The deepest layers of our skin contain around 70% water, and when in a healthy, hydrated state, the stratum corneum comprises around 20-30% water. Less than this, and our skin may appear dull, dry, and flaky, and its barrier function will be impaired.

We hydrate our skin in two ways:


  • Extrinsic hydration, which refers to the moisture that is added to the skin from external sources, such as cosmetic humectants, humidity in the air and water; and

  • Intrinsic hydration, which refers to the moisture that is naturally produced within the skin (we explain this below) and is affected by diet and water consumption.


The outer epidermal layer is far more than “dead” cells (corneocytes) as it is responsible also for managing the skin’s lipid barrier and its own natural moisturising factor (NMF). Lipid barrier and NMF are not the same thing. The lipid barrier contains fatty acids, ceramides and cholesterol, and the NMF contains humectants such as amino acids, urea, lactate, mineral salts and organic acids. We describe the NMF as hygroscopic because it attracts water to retain it in our skin. Hyaluronic acid, however, is not part of the NMF, but it is present in the dermis (the skin’s deepest layer).


The lipid barrier and NMF substances work together to maintain the skin’s hydration levels and prevent water loss. Cosmetic products work topically to assist our skin’s own capabilities.


Moisturize and hydrate have similar aims – to increase the skin’s hydration – but do so in different ways.

Moisturizing: To help the skin’s lipid barrier function well as a protective layer and be fully effective in preventing transepidermal water loss (TEWL), we use a moisturizer. It helps reduce TEWL by replenishing the skin lipids and aiding in their barrier function by providing an occlusive layer.


Hydrating: To help replenish the stratum corneum’s water content, we use hygroscopic (water-attracting) ingredients called humectants. They work by actively attracting more water to the skin and helping retain it within the skin to improve overall hydration levels.

From a cosmetic formulator’s viewpoint, the key difference between moisturizing and hydrating lies in the type of ingredients used, not necessarily in the name of the product. The word “moisturize” is somewhat misleading. To moisturize implies adding moisture, when in fact cosmetic moisturizers act to prevent water loss from the skin rather than add more water to it.


Moisturizers tend to be emulsions like creams, body butters and lotions, but the category also embraces gels and serums with more product types coming on the market every year. Moisturizers also include anhydrous products.


In cosmetic terms, “to moisturize” also means making the skin supple and smooth, and the emollients (oils and butters) in a typical moisturizer do just that. Let’s give some examples: squalene is naturally part of our sebum, and natural emollients like squalane (a plant-derived lipid) are used as an emollient and occlusive ingredient. Jojoba oil (a wax) has excellent biocompatibility with our skin, in effect mimicking substances in the lipid barrier.


However, depending on the percentage of water and water-based ingredients to oils and butters in a formula, an emulsion-based moisturiser clearly can add some water to the stratum corneum, even if its purpose is to lock moisture into the skin by creating an occlusive film and reinforcing the lipid barrier.


HUMECTANTS: Skin Care INGREDIENTS TO SUPER HYDRATE THE SKIN


Humectants, such as what is found in Sugie Cubes All Natural Body Scrub, work by drawing water from the environment into the skin and binding it to the skin’s surface. But, depending on the level of humidity in the air, they may also draw water from lower layers of the skin to the uppermost layer, the stratum corneum. In either case, the effect is similar as the humectant is acting to help improve the skin’s overall hydration levels and keep it looking plump and hydrated.


Sugie Cubes All Natural Body Scrub contains Hyaluronic acid (AHA), which is a powerful humectant that can hold up to 1000 times its weight in water. This makes it an excellent ingredient for hydrating the skin, as it can help to improve overall hydration levels and reduce the appearance of fine lines and wrinkles.

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