Like a medieval castle, the skin plays multiple roles: part defense, part regulatory hub, part sensory to keep a pulse on the outside world. This post examines the defensive barrier function of the skin and its role in inflammatory skin disease like contact dermatitis.
An Anatomy Lesson
As a visual learner and thinker, I find understanding the anatomy, or more precisely the microanatomy (aka: histology) of the skin is paramount to any discussion of skin disease. If one can “see” where the problem is, maybe one can better understand the treatment regimen. A few years ago, I commissioned a local artist to create a vintage school chart of the skin for my exam rooms (seen below) to aid in such discussions.
From the outside to the inside, the skin is composed of 3 layers: the epidermis on top, the dermis in the middle, and the hypodermis (or subcutis) below. The epidermis provides the barrier function of the skin while the dermis acts as a support structure with nerves, blood vessels, hair follicles, oil glands and sweat glands. The hypodermis (or fat layer) provides insulation and a soft padding over which the skin can move without disrupting the larger blood vessels and muscles below.
The EPIDERMIS Up Close
The top layer of the skin, or epidermis, is further divided into 4 layers: the stratum basalis which gives birth to the stratum spinosum where squamous cells differentiate toward dead corneocytes, the stratum granulosum which houses lamellar bodies that generate lipid precursors, and the stratum corneum where dead squamous cells form the most important layer of defense. This movement of the skin cells from the stratum basalis to the stratum corneum is call keratinization. This journey from the stratum basalis at the bottom through to desquamation from the stratum corneum at the top takes approximately 4 weeks.
A BRICK & MORTAR* approach to the STRATUM CORNEUM
The outermost layer of the epidermis is called the stratum corneum. It is composed of corneocytes (dead keratinocytes) as bricks held together by a lipid “mortar” composed of ceramides, free fatty acids, and cholesterol in a precise 3:1:1 ratio.
*Based on the work of Peter Elias, MD – Check out his blog here for more information on the importance of the skin barrier.
Barrier Function of the Skin
As the protective outer coating of the human body, skin plays the key role in keeping the outside world out and the inside world in. From the outside, it defends against ultraviolet (UV) light and radiation, temperature extremes, mechanical injury, as well as many different organisms (bacteria, fungi, viruses), and chemicals (both allergic and toxic) in our environment. Of greater importance, our skin plays a key role in water regulation: it keeps water INSIDE of us. As 60% of our weight is water, that is no minor feat. When transepidermal water loss (TEWL) increases, the barrier becomes weakened and the skin becomes more susceptible to mechanical injury, infection, irritation from various substances, and allergic problems including skin rashes.
A healthy barrier creates skin that is smooth and elastic, sheds regularly without scale and can respond to friction without cracking. A dysfunctional barrier is marked by dry cracked, itchy red skin.
Roles of Barrier Function
- Permeability Barrier:
The stratum corneum brick wall maintains water balance, a calcium gradient and an acid pH.
- Antimicrobial Barrier:
To combat yeast and bacteria, the stratum corneum maintains an acidic pH, generates antimicrobial peptides and possesses lipids (free fatty acids) with antibacterial activity.
- Antioxidant Barrier:
The epidermis protects against oxidative stress. Vitamin E is the main antioxidant, but requires Vitamin C and ubiquinol for regeneration.
- Immune Response Barrier:
Antimicrobial peptides and toll-like receptors of the innate immune system protect against foreign invaders, but when stimulated erroneously can promote inflammatory disease (e.g., rosacea and atopic dermatitis). Dendritic cells such as Langerhans cells provide immune surveillance and interact with T-cell regulatory system (where contact dermatitis begins
- Photoprotection Barrier:
Physically, the stratum corneum thickness provides reflectance of UV light. Additionally, pigment (melanin) in the stratum basalis offers UV protection. Antioxidants in the epidermis serve to decrease the oxidative stress caused by UV radiation.
*Adapted and simplified from Del Rosso JQ, Levin J. The clinical relevance of maintaining the functional integrity of the stratum corneum in both healthy and disease affected skin. J Clin Aesthet Dermatol. 2011;4(9): 22-42.
WHAT FACTORS INCREASE TEWL* and WEAKEN THE PERMEABILITY BARRIER
*TEWL = transepidermal water loss
What Happens When Our Barrier Is Chronically Weakened?
A Model of Progression from Normal Skin to Eczema
An external, or exogenous, insult to the stratum corneum causes increased TEWL (transepidermal water loss). Initially the barrier is visibly the same and manages to self-repair through the recruitment of more lipids into the stratum corneum. With continued insults, the stratum corneum becomes overstressed and suffers more TEWL. At this point visible changes of dull, rough skin with fine scaling and exaggerated skin lines begin. Further exogenous damage results in more TEWL and severe xerosis marked by thick large scales, decreased skin elasticity and linear fissuring (or cracks) in the skin. With continued external insults, more water is lost and the skin becomes inflamed with redness, scaling, flaking and itch. This is called asteatotic eczema, or dermatitis.
A well-formulated moisturizer can STOP this progression by replacing lost fats and recruiting more water into the stratum corneum.
How to Repair (or Optimize) Your Barrier
- Avoid irritants and known allergens.
- Avoid harsh soaps, cleansers, and alcohol-based toners on the skin. Natural lye soaps like Ivory and Dial are too good at cleaning the skin and strip the skin of essential fats. Choose gentle synthetic detergents (“syndets”) such as: Dove, Oil of Olay, Aveeno, Cetaphil, or CeraVe.
- Replace the stratum corneum lipids: Use a moisturizing cream or lotion that contains more than just an occlusive agent. Choose one with a mix of fatty acids, cholesterol and ceramides. The best time to moisturize is after baths/showers. Some of our OTC favorites include: CeraVe, Atopalm, Cheryl Lee MD True Lipids, SkinFix.
- Acidify inflamed skin with vinegar baths. Follow this link for details.
- Stop scratching! This only worsens skin irritation. Use OTC medicated anti-itch lotions, such as Sarna or CeraVe itch. Use prescription anti-inflammatory molecules such as topical immunomodulators or topical steroids as needed to control severe inflammation and itching.
- Daily sun protection: wear protective clothing and sunscreen with SPF 30 or higher.
- Increase dietary sources fatty acids via salmon or flax seeds or supplements such as borage seed oil, fish oil, evening primrose oil.
My Lessons Learned
A comprised skin barrier causes water loss (TEWL) that leads to dryness and inflammation of the skin = dermatitis. Dry/scaly/red skin is a sign that your barrier is broken. One of the most common causes of barrier disruption is over bathing and use of harsh soaps. Did my daily shampooing with an SLS*-containing shampoo send me down this path of chronic scalp pruritus and allergic contact dermatitis? Absolutely.
You can prevent the progression to eczema by caring for your skin with gentle cleansers and a well-formulated moisturizer to help your skin repair itself.
Do you suffer from eczema or contact dermatitis?
Read more below or contact us at Red River Dermatology at 318-442-9395 to discuss your dermatitis.
PART ONE: Accepting My Itch and Its Limitations: A Tale of Allergic Contact Dermatitis and Learning from Failure in 3 Parts
If you have ever suffered from a chronic itch, I hope this article gives you some hope or at least a laugh. As a dermatologist, the patients that challenge me the most are often the itchy ones. Unfortunately, as my personal experience reveals, things are not always as simple as they should be. Read article.
PART TWO: Accepting and Managing Allergic Contact Dermatitis
Once the itch and rash moved to my face, I had to accept my patch testing results and transition to a fragrance-free world. In this article, I discuss allergic contact dermatitis and resources for finding products free of common and specific allergens. Read article.