Skin Hydration: How Does This Work?

By Paul Fister, B.Bus (Mktg), Dip. Form. Chem., Member ASCC

Recently we got into a discussion with a cosmetic chemist about skin hydration. She questioned our emphasis on the skin’s hydro-lipidic barrier. She did not agree that the skin is waterproof. 

Adequate levels of hydration are the key to healthy skin. A lack of moisture in the skin invariably leads to symptoms that become increasingly severe unless remedial action is taken. Tight skin, rough skin and scaly skin are clear signs indicating trouble ahead.

A quick search on the web will reveal a number of suggestions on how to increase hydration levels in our skin. Here are some examples:

  1. Drink more water.
  2. Take supplements with Essential Fatty Acids.
  3. Use ingredients like Hyaluronic Acid to draw water into the skin.
  4. After a shower, apply lotion to the skin while still damp to lock in moisture.
  5. A good moisturiser will supply water to the skin.
  6. The skin looks after itself. According to some US dermatologists, moisturisers are unnecessary or even counterproductive.
  7. Others say that all moisturisers are the same.

Here at Omniderm, this is what we have been teaching Australian aestheticians for over 20 years:

  • Our skin is waterproof. The hydro-lipidic barrier combined with the lipid bilayers in the Stratum Corneum will not allow water to penetrate. This is confirmed by a number of sources. 1 2
  • Our epidermis is avascular. It is the only organ that is not supplied with blood, and therefore does not obtain its moisture in the same way as other organs (Graphic P.1 illustrates the vascular system. Blood supply stops at the dermal/epidermal junction).
  • Moisture is supplied to the basal layer of our epidermis via diffusion through the dermal/epidermal junction.
  • Our epidermis constantly loses moisture to the environment through evaporation. This is known as perspiratio insensibilis (insensible perspiration). We lose around 600 – 800ml of water per day through this slow and steady process that we are not physically aware of. This is separate from sweat.

Graphic P.1. Source: BASF Personal Care and Nutrition GmbH

Ok, so we have moisture transferring from the dermis into the epidermis, and moisture being lost from the epidermis into the environment through insensible perspiration. If we accept that the skin is waterproof, that no moisture can penetrate from outside – what then is the critical factor that ensures natural healthy levels of hydration within the epidermis?

The answer is ‘balance’. In essence, water delivered from the dermis to the epidermis must equal the amount of water lost from the epidermis via Trans Epidermal Water Loss (TEWL). An excess of TEWL will, by definition, lead to dehydration of the skin.

Keep in mind that the amount of moisture entering the epidermis from the dermis is fixed. By contrast, water lost from the epidermis can fluctuate greatly, depending on the state of the skin barrier. So how does our skin maintain the balance between moisture gained and moisture lost? Nature has given it a tool that enables it to adjust TEWL to natural healthy levels. We used to call it the ‘acid mantle’. Today it is more commonly referred to as the ‘hydro-lipidic permeability barrier’. What exactly is it?

Sebum from our sebaceous glands combines with water in the Stratum Corneum to form what we refer to as the only TRULY NATURAL skin care cream. How does our skin achieve this, given that water and oil don’t mix? The answer: sterols, nature’s own emulsifiers. Sebum contains about 30% choleSTEROL. This enables oils and waxes from sebum to combine with moisture present in the Stratum Corneum, thus forming this amazing combination we know as the hydro-lipidic permeability barrier (see graphic P.2).

Graphic P.2. Source: BASF Personal Care and Nutrition GmbH

It should be noted that not everyone agrees with this theory.

A prominent US dermatologist stated in a book published in 2005: “Sebum has no known function.”3 This opinion was reconfirmed in a book in 2011: “The function of sebum is not known. It appears to have no function.”4 A bit further down on the same page there is some discussion on ‘sebum as barrier substance’ so it seems that the position on the subject might have been under review.

Mark Lees, PhD, writes: “The purpose of sebum is controversial. Some scientists think it is secreted as an additional surface barrier to help prevent skin dehydration. Some think it is a leftover from human evolution. Some think that it has no real purpose. What is known is that the skin that is alipidic (does not produce much sebum) has a strong tendency to become dehydrated, which supports the first theory.”5

We are firmly in the camp of sebum being a vital component of the skin barrier.

So, in our opinion, what does this ‘hydro-lipidic permeability barrier’ do?

Its main function is to slow moisture loss from the Stratum Corneum to match the moisture coming up from the dermis. (see Graphic P.1)

The hydro-lipidic barrier is extremely responsive to changes, as explained by Carl R. Thornfeldt, MD:

When the TEWL increases by as little as 1%, physiologic signals induce barrier repair by initially up-regulating lipid synthesis.”6

In other words, a minute increase of just 1% in Trans-Epidermal Water Loss will cause the skin to immediately increase its production of sebum in an effort to fortify its hydro-lipidic barrier. Why this rapid response? Loss of moisture from the skin is literally a survival issue. Without the hydro-lipidic barrier we would dry out like a prune.

So here we have it. We believe that the epidermis cannot be supplied with moisture from the outside. Rather, the epidermis obtains it from the internal blood supply via the dermal/epidermal junction. Our skin’s hydro-lipidic barrier is tasked with conserving this moisture by slowing evaporation to natural healthy levels, balancing moisture obtained from below with moisture lost into the environment.

In my next article we will discuss the role of moisturisers, the pros and cons of different types of moisturisers and their interaction with the skin and its hydro-lipidic permeability barrier.

Author’s Note

Good choices are based on good information.

We are told that some skin care brands focus their training solely on their product and on their ingredients. This gives you less than half the picture. The most important aspect of formulating an effective skin care product is to first understand how the skin functions. This ensures that the product does not interfere with, disturb or disrupt the skin’s natural functions but rather supports them and works with them. We call this the ‘biomimetic approach’. A lack of understanding of skin functions can lead to products and treatments that address symptoms rather than causes.


  1. Mylady’s Standard Cosmetology, Delmar Learning, p.122
  2. Physiology of the Skin, Zoe Diana Draelos, MD and Peter T. Pugliese, MD, Third Edition, ISBN: 978-1-932633-77-1, Allured Business Media, Carol Street, IL 60188, p.2
  3. Advanced Professional Skin Care Medical Edition, Peter T. Pugliese, MD, ISBN 0-9630-2113-3, The Topical Agent LLC, 7147 Bernville Road, Bernville, PA 19506, p.73
  4. Zoe Diana Draelos, MD and Peter T. Pugliese, MD, op cit, p.64
  5. The Skin Care Answer Book, Mark Lees, PhD, First Edition, ISBN-13: 978-1-4354-8225-8, Cengage Learning, Milady, Executive Woods, 5 MAXWELL Drive, Clifton Park, NY 12065 USA, p.11
  6. The New Ideal in Skin Health: Separating Fact From Fiction, Carl R. Thornfeldt, MD and Krista Bourne, LE, ISBN: 978-1-934633-69-6,  Allured Books, Carol Stream IL 60188, 2010, p.172.

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