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How Do Moisturizers Work? Your Guide to Ingredients

A good moisturizer is key in preventing and treating dry skin, and this is doubly true for people with any kind of eczema. We all know that moisturizers are important, and we know they work. Have you ever thought about how they work? 

Below is a list of some of the most common ingredients found in moisturizers, as well as a brief description of what they do and how they do it. 

What Are Moisturizers?

In one National Institute of Health (NIH) paper, moisturizers are described as “topically applied products designed to increase the water content of the skin.”

The paper goes on to say, "Ingredients used in these products have a range of actions, including preventing transepidermal water loss and promotion of desquamation.”

In other words, moisturizers work in several different ways, depending upon their ingredients, to keep water from evaporating from skin cells (transepidermal water loss) and to promote the shedding of dead, dry skin cells (desquamation). 

By preventing transepidermal water loss (TEWL), moisturizers support the health of the skin barrier. In many cases, moisturizers must do the work that a compromised skin barrier cannot do on its own. The science of moisturizers begins with a basic understanding of the skin barrier

The Skin: A Barrier to the Outside

Your skin is the first barrier between you as an organism and the outside world. It’s designed to keep harmful things (radiation, pathogens, and irritants) out while keeping beneficial things (like moisture and nutrients) in. 

The skin has three primary layers: the epidermis, the dermis, and the hypodermis. Each plays its own role in protecting you from external influences. It is the outermost layer–the epidermis–that concerns us today. 

The epidermis itself comprises seven layers: 

  • The stratum basale (the deepest portion of the epidermis)
  • The stratum spinosum, 
  • The stratum granulosum,
  • The stratum lucidum, 
  • The stratum corneum (the most superficial portion of the epidermis).

Keratinocytes are the most common kind of skin cell found in the epidermis, comprising 90% of the skin cells in this layer. They are made in the stratum Basale and secrete a tough, fibrous protein called keratin, as well as a protein called filaggrin.


skin barrier three layers of skin

Through a process called differentiation, the keratinocytes migrate through each of the upper layers of the epidermis, changing form at each stage until they’re pushed up to the outermost layer of the epidermis (the stratum corneum).  

The Barrier’s Barrier

In the stratum granulosum, keratinocytes begin to produce more and more keratin. They are flattened into interlocking diamond shapes, then journey upwards into the stratum corneum, where they are flattened even more. 

In the stratum corneum, the keratinocytes become corneocytes, losing their nuclei and organelles. The corneocytes lock together like bricks to create a hard, physical barrier over the epidermis. 

The filaggrin the keratinocytes secreted acts as a somewhat waterproof mortar between these interlocking cells. It keeps the corneocytes connected and protects the epidermis from external water molecules while preventing the evaporation of moisture from the epidermal cells.  

This layer of flattened keratinocytes and filaggrin make up a physical barrier, preventing large molecules from passing through the skin cells from the outside. 

Nature’s Moisturizer

The filaggrin does more than contribute to a physical barrier. The corneocytes are hydrated by natural moisturizing factor (NMF), which is made up of amino acids and lipids, urea, sugars, and fatty acids produced by filaggrin.

The NMF draws water from the atmosphere to keep the corneocytes hydrated and flexible until it is time for them to be shed and replaced. The NMF changes its viscosity in response to external stimuli, providing more or less hydration as needed. In normal skin, NMF can adjust to even extremely arid environments, keeping the skin hydrated and nourished. 

This is all the product of the filaggrin’s response to the environment. If environmental conditions are dry or otherwise harsh, the filaggrin will break down and create more NMF. Otherwise, it will remain stable. 


normal and damaged skin


Modern topical moisturizers typically try to mimic selective properties of both the skin’s physical barrier and the NMF. Their ingredients have different mechanisms, depending upon what the customer needs. 

Three Basic Kinds of Moisturizers

Moisturizer ingredients typically fall into one of the following categories: occlusives, humectants, and emollients. Most moisturizers utilize more than one of these ingredients; some ingredients, like glycerin, manage all three roles. 


  • Occlusives are heavy lipids that sit on the skin’s surface and prevent water from evaporating from the surface of the skin. Occlusives tend to have a thick, creamy consistency. 


  • Petrolatum (petroleum jelly or VaselineⓇ), beeswax, mineral oil, and dimethicone are all examples of occlusives. Mink oil, emu oil, and lanolin are some others. 

  • Emollients: While the difference between emollients and occlusives is somewhat arbitrary (and some would say artificial), skincare professionals usually define emollients as ingredients that soften the skin and allow water molecules to enter skin cells more easily. When defined this way, emollients usually have a lighter consistency than occlusives. Vegetable oils such as coconut oil, castor oil, olive oil, and grape seed oil were probably some of the first emollients used by humans.

  • Humectants are chemicals that draw water molecules into the skin cells. When the humidity is more than 70%, humectants can draw moisture from the air into the skin. Usually, though, they will draw water upwards from deeper layers of the epidermis and dermis.

Some common humectant ingredients in moisturizers include: 

  • urea, which is a component of the NMF. Urea improves absorption of water into the stratum corneum and promotes the shedding of dead skin cells. It also helps topical medications penetrate the skin more efficiently. 

Urea reduces and improves itching, making it a useful ingredient for people with eczema, hyperkeratosis, and other drying skin disorders.

  • Alpha-hydroxy acids (AHAs), including glycolic and lactic acids. These ingredients affect the hydration of the stratum corneum in a variety of ways: attracting water molecules, encouraging dead skin cells to shed, and increasing levels of ceramides. 

  • Glycerin is a common ingredient in skincare products. It attracts and binds water and helps repair the skin barrier. Other humectants include honey, propylene glycol, sorbitol, and hyaluronic acid

Some ingredients manage all three roles at once, making them useful for a wide variety of skincare needs. Glycerin, for example, is a powerhouse that acts as a humectant, emollient, and humectant at once.

The Science of Moisturization

People sometimes speak about choosing a moisturizer as a question of choosing whether they need a humectant, an occlusive, or an emollient. In reality, it is not that simple. 

It seems intuitive to add a humectant to dry skin. However, if the air is not adequately humid, the humectant can actually contribute to TEWL. They should be used with an occlusive or an emollient. 

Similarly, in the absence of a topical humectant, an occlusive adds no moisture to the skin. It would prevent TEWL, but this is a moot point if there is not enough water in the cells to begin with. As water migrates to the epidermis from deeper levels of skin, dryness would improve–but this process takes days. 

The solution is in finding a product that addresses all of your skin’s specific needs. If you are prone to oily skin and acne, then a lotion containing a humectant and a lightweight emollient is probably your best bet.

 If your skin is dry, a heavier lotion with more humectants and strong occlusive (like petrolatum) is probably better. Ointments usually work better than everyday creams or lotions for those with active eczema flares.

Is There a Single Product That Does It All? 

Helping patients battle eczema inspired board-certified dermatologist Steve Harlan, MD to develop a steroid cream that would relieve inflammation without the risk of skin atrophy and topical steroid withdrawal when used properly. SmartLotionⓇ is the result of his expertise and dedication to his patients. 

Dr. Harlan now brings us HarlanMD Perfect Repair™ moisturizing cream, a complete solution to complicated moisturization needs. 


perfect repair

Each ingredient in Perfect Repair™ was chosen to prevent irritation and improve skin barrier function. It is fragrance free and does not use harsh emulsifiers. 

Perfect Repair™ is loaded with natural ceramides. It also contains coconut oil for its powerful healing benefits and occlusive properties. Perfect Repair™ uses glycerin, an exceptional humectant as well as an emollient, to hydrate and soften the skin. . 

Like SmartLotionⓇ our eczema cream, Perfect Repair™ incorporates prebiotic ingredients to balance your skin’s microbiome. 

Because it leverages Dr. Harlan’s intimate knowledge of the skin barrier and the NMF, Perfect Repair™ benefits a wide variety of skin types. It is non-comedogenic and hypo-allergenic. It is neither heavy nor oily, but it is still an exceptional defense against TEWL.

Perfect Repair™ offers skin-softening emollients, occlusives, and moisture-adding humectants in one easy-to-use product. Containing no harsh fragrances or emulsifiers, it really is the perfect moisturizer for those with dry or sensitive skin. 



  Cee Van

  Medical Writer



Ashley - Customer support

Hi SS,
Perfect Repair ™ does not contain any steroids :-) Our SmartLotion eczema cream does contain low-dose hydrocortisone. If you’d like more information please feel free to reach out to us at support@harlanmd.com


Does it contain any steroid components?

Ashley - Customer support

Hi all! Thank you so much for your interest in HarlanMD’s new prebiotic complex moisturizer, Perfect Repair™! It is available on our website now!


If you have any additional questions or need any help, don’t hesitate to reach out to us at support@harlanmd.com

Jo Ann

When can I try the moisturizer I love the smart lotion.

Ashley - Customer support

Hi all!

We will have Perfect Repair available to purchase on our website soon!

We’re very excited to offer this new moisturizing option to our customers and we hope you love it!

Stay tuned for more information. We will be sending out an email once it’s available in the next few weeks.

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