Moisture barrier, lipid barrier, skin barrier, acid mantle – there are multiple names to describe the outermost layer of skin that acts as a protective force against external aggressors and consequently maintaining the integrity and health of our skin. With the rise in availability and misuse of topical treatments such as retinoids and chemical exfoliants, there is an epidemic of impaired barrier function, both minute (slight dehydration) and severe (sensitised skin, conditions such as dermatitis, acne, etc). Here’s cheat sheet 1 on how our moisture barrier works!
What is the stratum corneum?
The stratum corneum is the outermost layer of the epidermis and its primary function is to form a barrier and protect underlying tissue from external aggressors. This can range from environmental stressors such as weather, pollution, sun exposure, infection or protect against topical irritants such as harsh surfactants, aggressive treatments (retinoids, exfoliation) or potentially sensitising ingredients (essential oils, fragrance). How well the stratum corneum functions can also depend on internal factors such as age and hormones. In simple terms, the stratum corneum works to keeps the good stuff in and the bad stuff out. How does it do this?
What are lipids?
The stratum corneum is comprised of corneocytes (dead skin) embedded in a lipid matrix (long chain ceramides, free fatty acids and cholesterol, the optical mixture of which is 50% ceramides, 25% cholesterol and 15% free fatty acids). Why are they important? Lipids create a water-impermeable and homogenous barrier that effectively prevent transepidermal water loss. The depletion of this lipids (that make up a huge part of the stratum corneum!) can cause dryness, burning/stinging sensations, flakiness, amongst other undesirable symptoms.
What is TEWL?
Transepidermal water loss (TEWL) is as the name suggests: the loss of water from the stratum corneum. Skin with low water content or a high susceptibility to TEWL (from impaired barrier function) ultimately results in less pliable skin, causing a range of issues from dryness, pronounced fine lines and overall texture, increased oil production, increased breakouts. ‘Dehydrated’ skin, as we know it, is caused by either a lack of water altogether, or the inability for skin to hold on to that water. (More on this later!)
What is NMF?
Natural Moisturising Factor (NMF) is a ‘protective coat’ that helps skin maintain elasticity, reduces TEWL, regulates desquamation and is essential to the integrity of the stratum corneum. NMFs are hygroscopic (water-loving) substances, including amino acids, Urea, sugars, minerals, salts, etc. See the handy chart below of NMF components!
I feel as though NMF are much more underrated than lipids such as ceramides – despite also playing a crucial role in skin barrier function. Just like the lipids present in our skin, NMFs can deplete due to environmental stressors, age, hormones, aggressive topicals, etc. Reduced levels of NMF have been associated with psoriasis, eczema, or xerosis (dry skin) – conditions that are generally linked to abnormal desquamation.
What is desquamation?
Desquamation, or more commonly known as keratinization, is the shedding of dead skin cells.
What does this all mean?
It means that our moisture barrier is made up of substances that are quite easily depleted, by our own doing or by factors we cannot control (age, weather). Given that these components can be depleted, I think its important to compensate by either incorporating these substances topically, or changing our habits to prevent impaired barrier function in the first place (but preferably both!).
What can cause impaired barrier function?
You may have guessed!
- Internal factors: Age, hormones, diet, lifestyle (smoking, stress, etc).
- External factors: Weather, pollution, sun exposure, infection, topicals.
YOU SHOULD NEVER FEEL DRY OR TIGHT AFTER CLEANSING (repeat it for the people at that back)
- Cleansers are one of the main causes of impaired barrier functions. The issue with surfactants in cleansers is that their components can bind to stratum corneum proteins and solubilise lipids, enzymes, and natural moisturizing factors. Surfactants can also remain in the stratum corneum even after the removal of a cleanser, causing chronic surfactant exposure which (surprise!) leads to impaired barrier function. Even with the most gentle of surfactants, they are still removing essential components from the skin, yet cleansing is absolutely necessary. Our best bet is to choose cleansers that boast a range of emollients or ‘lipid layer enhancers’ that can alter the irritation potential of surfactants. I’m working on an extensive blog post R.E Cleansers and Surfactants that will explain this in more detail. (I’ll link here once published!)
- Another factor to consider with cleansers is their pH. Our skin’s ‘acid mantle’ is slightly acidic (can range from pH 4.5-5.5) and maintaining this acidic environment improves the permeability of our skins barrier, allows for ‘normal’ desquamation and promotes the growth and balance of healthy bacteria. A cleanser that fits in this range (my preference is around pH 5-5.5) is a viable way of negating potential side effects of cleansing.
Overuse, misuse, combining too many active treatments; despite their stunning results, active ingredients can unfortunately impact our barrier function. Below is a non-exhaustive list of the most popular active ingredients.
- Exfoliants (physical or chemical I.E AHA, BHA, PHA, enzymes, TCA, high strength peels)
- L-Ascorbic Acid
- Azelaic Acid
- Benzoyl Peroxide
If you are struggling with sensitised skin, they are best avoided until your moisture barrier is restored.
This is going to vary – some people react to essential oils and fragrance, others don’t.
Symptoms of impaired barrier function
Symptoms are going to vary per person, but below are some common characteristics of an impaired barrier:
- Dryness, flakiness
- Stinging or burning sensations when applying products
- Excess oil production
- Excess breakouts – both inflamed and closed comedones
- Dehydration/TEWL – skin feels tight (particularly after cleansing or as the day progresses)
- Redness, flushing and increased sensitivity
- A waxy, almost ‘satin wrap’ appearance, with or without the presence of oil
- Increased texture – ‘orange peel texture’
- Larger pores
Next up is part 2 that discusses dry vs. dehydrated skin, and why hydrating layers may not ‘fix’ your dehydration!