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Examining The Structure of Skin

Book Extract

This article is an extract from: Seborrheic Dermatitis - The Owner's Manual; a book dedicated to understanding seborrheic dermatitis. See the book overview page for more information.

The skin is actually composed of various layers, and each layer plays a crucial function in the overall function of the skin as a whole. Issues in each of the skin’s layers can produce a domino effect and can contribute to breakdown in the overall health of the skin.

The Structure of Human Skin - Epidermis, Dermis, Hypodermis

The Epidermis

A good way to think of the surface of the skin (epidermis) is to imagine a layer of bricks and mortar: the bricks being special skin cells called keratinocytes and the mortar being a protein by the name of collagen. But unlike bricks, keratinocytes initially form deep within the skin, make their way to the top, and then die and shed off.

A Closer Look at the Epidermis - Kertatinocytes

The rate of this epidermal turnover in healthy individuals typically takes about 48 days [1]. Since this process is ongoing, it becomes essential for the body to produce healthy collagen and keratinocytes.

In certain skin conditions such as seborrheic dermatitis [2], psoriasis and various others, this process occurs at a drastically increased rate. This increased rate creates challenges for healthy cell production and more chances for immature cells to make it to the front lines. Since the skin is one of the body’s largest organs, this process can create an imbalance throughout the whole system.

Increased rate of epidermal turnover in psoriasis
Some studies suggest the rate of epidermal turnover can be as rapid as only 6-8 days in psoriatic skin. And this is roughly 6 times faster then healthy skin [3].

To get a good understanding of how much is really going on, consider the fact that the skin of an adult occupies an area of about 1.5-2 square meters and can make up about 16% of total body weight. Additionally, each square centimeter of skin is home to about 6 million cells, 100 sweat glands, 15 sebum glands, 400 cm of nerve fibers alone, and much more. This isn’t even considering the vast communities of microorganisms that call our skin their home.

The Sweat Glands

The epidermis is home to two types of sweat glands. One of these sweat glands is called the eccrine, while the other is called the apocrine.

Eccrine sweat glands are distributed practically across the entire skin surface and play a major role in thermoregulation through the secretion of sweat comprised mainly of water, salt and electrolytes. In order to protect this sweat, the acidity of the sweat has to be just right, and crucial antimicrobial peptides (such as cathelicidin and b-defensins) must be present.

Several studies have demonstrated that a variety of skin conditions may be a direct result from the absence or reduction in the number of antimicrobial peptides or other issues in the composition of the sweat [4, 5]

On the other hand, the apocrine sweat glands have a more limited presence. These sweat glands are mainly found inside the armpit, around the genitals, and the anus. Even though they exist from birth, they only become active during puberty and thereafter. These glands secrete a more oily liquid of mainly proteins, lipids, and steroids into the hair canal. It’s the consumption of this liquid by bacteria that produces the smell that we all associate with sweat.

The Sebaceous Glands

The sebaceous glands are directly connected to our hair follicles. Together, they form what is called the pilosebaceous unit (basically the gland and the hair follicle). These glands secrete a lipid-rich substance called sebum. Sebum plays a crucial role in lubricating the hair and skin.

The composition of sebum mainly consists of triglycerides, wax esters, squalene, cholesterol, antimicrobial peptides and antimicrobial histones. The oily nature of sebum makes it a target of a fairly large number of oil dependent bacteria, such as propionibacterium acnes and malassezia yeasts. To defend against this, the skin relies on the breakdown of triglycerides to antimicrobial free fatty acids and an adequate supply of antimicrobial peptides and histones.

Failure of the sebum to defend against opportunist bacteria and yeast has long been considered the cause of a variety of skin issues [6, 7, 8]. Since the sebum is secreted alongside hair follicles, it becomes an excellent site for bacteria to penetrate below the acid mantle.

The Acid Mantle

Above the epidermis, we have what is called the acid mantle. This is the very thin layer of “stuff” that sits on the epidermis. Typically, it is comprised of lipids, amino acids, sebum, sweat, hormones, lactic acid and various micro-organisms.

This layer is crucial and serves as a fundamental top layer of protection, ensuring that pathogenic bacteria don’t have a chance to proliferate and cause havoc. If this layer is successful at doing it’s job, the epidermis has much less work to do and no inflammation is less likely to occur.

Section Summary

This section provided a closer examination of the skin and some of the most relevant and problematic components. Key points include:

  1. Skin is made up of several components (layers) and proper functioning of each layer is essential to healthy skin
  2. The top most layer of the skin is called the epidermis and this can be the most problematic area because of it’s direct contact to the outside world
  3. The epidermis is primarily composed of cells called keratinocytes which are formed deep within the skin and make their way to the exterior where they die
  4. In certain skin conditions (including seborrheic dermatitis) the rate of epidermal turnover is drastically increased and this may be a core component of these conditions
  5. The epidermis uses various liquids, such as sweat and sebum, to regulate it’s environment and and protect it from external threats
  6. Sweat contains a mix of antimicrobial peptides and it’s pH is carefully regulated to protect the skin from infection
  7. Sebum is a mix of triglycerides, wax esters, squalene, cholesterol, antimicrobial peptides and antimicrobial histones
  8. Deficiencies in individual components of sweat or sebum have been linked to improper barrier function, increased rates of infection and skin disease

Book Extract

This article is an extract from: Seborrheic Dermatitis - The Owner's Manual; a book dedicated to understanding seborrheic dermatitis. See the book overview page for more information.


  1. Maranke I Koster "Making an epidermis." Annals of the New York Academy of Sciences 1170 (2009): 7-10. PubMed
  2. G A Turner, M Hoptroff, C R Harding "Stratum corneum dysfunction in dandruff." International journal of cosmetic science 34.4 (2012): 298-306. PubMed
  3. K M Halprin "Epidermal “turnover time”–a re-examination." The British journal of dermatology 86.1 (1972): 14-9. PubMed
  4. Maugorzata Marcinkiewicz, Suawomir Majewski "The role of antimicrobial peptides in chronic inflammatory skin diseases." Postepy dermatologii i alergologii 33.1 (2016): 6-12. PubMed
  5. Siegbert Rieg, Heiko Steffen, Silke Seeber, Andreas Humeny, Hubert Kalbacher, Klaus Dietz, Claus Garbe, Birgit Schittek "Deficiency of dermcidin-derived antimicrobial peptides in sweat of patients with atopic dermatitis correlates with an impaired innate defense of human skin in vivo." Journal of immunology (Baltimore, Md. : 1950) 174.12 (2005): 8003-10. PubMed
  6. A Yamamoto, S Serizawa, M Ito, Y Sato "Stratum corneum lipid abnormalities in atopic dermatitis." Archives of dermatological research 283.4 (1991): 219-23. PubMed
  7. Byung In Ro, Thomas L Dawson "The role of sebaceous gland activity and scalp microfloral metabolism in the etiology of seborrheic dermatitis and dandruff." The journal of investigative dermatology. Symposium proceedings / the Society for Investigative Dermatology, Inc. [and] European Society for Dermatological Research 10.3 (2005): 194-7. PubMed
  8. C C Zouboulis, E Jourdan, M Picardo "Acne is an inflammatory disease and alterations of sebum composition initiate acne lesions." Journal of the European Academy of Dermatology and Venereology : JEADV 28.5 (2014): 527-32. PubMed
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About Michael Anders

After being affected by seborrheic dermatitis, I have made it my goal to gather and organize all the information that has helped me in my journey.

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