Understanding the Skin Barrier

By Dr Tara Francis / 19 Nov 2022

Dr Tara Francis provides an introduction to the skin barrier and its relevance to aesthetic practitioners

The human skin comprises three main layers: the epidermis (outermost layer), the dermis (middle layer) and the subcutaneous layer. The most upper layer of the epidermis is the stratum corneum, and is typically given a likeness to a ‘brick and mortar’ arrangement microscopically; the bricks being corneocyte cells, and the mortar being fats such as ceramides, cholesterol and fatty acids.1 The stratum corneum (SC) acts as a skin barrier and is the body’s first line of defence to the percutaneous penetration of exogenous substances, both accidentally encountered as well as deliberately (outside-inside barrier), whilst also allowing your body to retain water and other components of the body (inside-outside barrier).1,2 

The barrier to water permeation is not absolute and the normal movement of water through the SC into the atmosphere is known as transepidermal water loss (TEWL). Any changes in the cellular composition and arrangement results in altered barrier function, leading to conditions such as eczema and psoriasis, as well as symptoms such as dry skin, sensitive or inflamed skin, pigmentation, wrinkles and infection.1,2 

It’s important as medical practitioners we are educated and knowledgeable on the skin barrier function, as some patients are compromising theirs. Some of the treatments we carry out in-clinic could also be contributing to damage.

Causes of skin barrier damage 

Potential causes of skin barrier damage include:1-2 

  • Environmental factors – dry or humid environment, hot or cold weather, allergens, pollutants, cuts or wounds 
  • Lifestyle factors – smoking, too much sun exposure, hot baths or showers, an unhealthy diet, lack of sleep, stress, poor skincare 
  • Patient factors – family history of skin conditions, ageing, ethnicity 
  • Iatrogenic factors – certain prescribed medications such as steroids, treatments in-clinic such as chemical peels, laser, microneedling, inappropriately prescribed active ingredients for topical use 
  • pH – normal human range of the stratum corneum pH is 4.5-5.5, and higher pHs have been associated with acute dermatitis

How to protect the skin barrier

As we know, prevention is better than cure, and so protecting the skin barrier should be the practitioner’s aim. Below is some advice we can pass onto our patients.

Avoid excessive sun exposure

Patients should avoid too much sun exposure because UV rays can cause cellular damage. As such, we should recommend that our patients use a broad-spectrum sunscreen, minimum SPF 30, and reapply throughout the day or after swimming and sweating. In my experience, mineral sunscreens are better than chemical sunscreens for some patients, such as those who suffer with rosacea. This is because mineral sunscreens sit on the skin and block UV rays, whereas chemical sunscreens will absorb active ingredients that deactivate UV rays, which can cause heat and therefore irritation.4

Have a healthy diet

Practitioners should encourage their patients to include nutritious foods in their diet. For example, recommend foods that contain omega-3 fatty acids (like oily fish and flaxseed) as these can improve TEWL and skin hydration. Avocados also have the potential to protect skin from sun damage through some of the compounds they contain.5 Another example is broccoli, as this contains a compound called sulforaphane, which can protect against sun damage by neutralising harmful free radicals. Practitioners should become aware of how eating habits impact the skin’s barrier and there are many good resources available to build knowledge in this area.5,6,7

Consider other relevant lifestyle factors

Patients should try not to irritate their skin with long hot baths, pat dry their skin with a towel instead of aggressively rubbing, and to pick spots or scabs. This is because the break in skin causes a defective barrier and also allows bacteria into the skin, which can cause irritation.8 Patients should also try to manage stress levels where possible – a study carried out on 25 healthy women suggests that one mechanism contributing to stress-induced exacerbation of some chronic hyperplastic and inflammatory skin disorders is stress-induced impairment of skin permeability barrier homeostasis.9 The same study showed that there was a significant reduction in skin barrier function recovery after sleep deprivation, so practitioners should advise patients to try and get enough sleep consistently. The generalised and known recommended amount is seven to nine hours of actual sleep, rather than simply resting in bed.9

Look into skincare


The term ‘moisturiser’ implies that the substance applied adds water and/or retains water in the SC. This is true for many of the products in use today, although the mechanism by which this is accomplished may vary. Urea, propylene glycol, glycerin and hydroxy acids (especially lactic acid) are humectants (water holding) and are used in many moisturising formulations; however, they all also function as exfoliants (they promote desquamation).10 Another mechanism for moisturising skin is to provide an exogenous barrier to TEWL so that more water is retained in the SC – a ‘barrier cream’. This is the mechanism by which petrolatum works.10


Formulations that include ceramides are extremely beneficial to protecting the skin barrier function. Research shows that products containing pseudo-ceramides may help improve the dryness, itchiness and scaling caused by a poorly functioning barrier.11 Ceramide-rich moisturisers may also strengthen the structural integrity of the skin barrier.10


When applied topically, constituents of lipids (plant oils such as triglycerides, phospholipids, free fatty acids, phenolic compounds and antioxidants) may act synergistically by several mechanisms:13

  1. Promoting skin barrier homeostasis
  2. Antioxidative activities
  3. Anti-inflammatory properties
  4. Direct and indirect anti-microbial properties
  5. Promoting wound healing
  6. Anticarcinogenic properties. Some of the most effective plant oils include coconut oil, jojoba oil and almond oil


Niacinamide, a form of vitamin B, can help to decrease inflammatory activity, decrease TEWL and increase SC thickness. In one study of 20 healthy patients, areas treated with formulations containing niacinamide were significantly different to pre-treatment baseline and untreated/vehicle-control treated sites, with larger and more mature corneocytes.14


Enzymes in the SC function optimally in an acidic environment and are responsible for the production of ceramides and free fatty acids which affect diffusion through the epidermis. The acidic skin surface, together with an intact SC, prevents colonisation with pathogens and supports the normal skin microbiome.2 As the clinical benefits of acidification are becoming increasingly evident, wherever possible or appropriate, reduced pH emollients and cleansers should be deployed to prevent and treat acute dermatitis.15

Creating a plan for your patient

In my opinion, when consulting patients, you should always gain a thorough understanding of the patient’s skin history, lifestyle, medical history, diet, habits and current skincare regimes.

My advice is to repair the barrier function as best as possible before carrying out any in-clinic treatments such as skin peels, microneedling or heat-based treatments, and before prescribing any active ingredients. This is done by applying knowledge from the guidance above and stripping back to only necessary high quality skincare products – a cleanser, a moisturiser and an SPF is important in my view. I have found that once the skin barrier is functioning better, healing will be quicker after treatments and results will be more effective. When introducing active skincare ingredients, I advise to go slowly and create a gradual approach so as not to over challenge the skin barrier.

Focus on skin health

The skin is a complex organ and the skin barrier has many intricacies in its makeup, cellular activity and influencing factors. What has been mentioned in this article is just a brief snippet of the science behind the skin barrier. There is yet more to be discovered, and more to be investigated, however, from research to date it is clear of some of the things that disrupt the barrier and things we can do to protect it.

Our role as medical aesthetic practitioners is to treat the patient as a whole. Most patients come to us with the desire to minimise the signs of ageing or to help with their appearance, including skin quality. However, keeping the skin barrier healthy is an absolute responsibility on our end, as it is not just an aesthetic concern, it is also an overall health concern. 

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