What is transepidermal water loss (TEWL)? How to protect your skin barrier in Summer.

Summer brings longer days outdoors, golden light, warmer temperatures, water activities and often more travel. While many of us associate the season with healthy, radiant skin, it can also place the skin under considerable environmental stress. If your skin suddenly feels tighter, drier or more sensitive than usual, increased transepidermal water loss (TEWL) could be the reason. Here's everything you need to know about this natural process and how to support optimal skin health throughout the season.

What is transepidermal water loss?

The skin's outermost layer, known as the stratum corneum, acts as the body's protective shield. Often described as a "brick-and-mortar" structure, it consists of skin cells (the bricks) held together by a matrix of lipids (the mortar), including ceramides, cholesterol and essential fatty acids.¹ Together, they regulate how much water escapes from the skin while protecting it from external aggressors. A small amount of water naturally evaporates through the skin every day. This process, known as transepidermal water loss (TEWL), is entirely normal and essential for healthy skin function. Problems arise when the skin barrier is weakened. As its lipid matrix becomes disrupted, moisture escapes more rapidly than it can be replenished, leaving skin feeling dehydrated, tight and increasingly vulnerable to environmental and oxidative stress.

For this reason, TEWL is one of the most widely used indicators of overall skin barrier health. The greater the water loss, the more compromised the barrier is likely to be.

Why does TEWL increase during summer?

Summer exposes the skin to a unique combination of environmental stressors that can accelerate moisture loss. Intense UV exposure, high temperatures, air conditioning, travel, dry cabin air, chlorine, salt water, sweating and frequent showering all place additional pressure on the skin barrier. These constant changes can disrupt the skin's protective lipid structure, allowing water to evaporate more readily, thus increasing transepidermal water loss. As hydration declines, skin starts sending signals, such as dryness, tightness, sensitivity or discomfort, despite warm and humid weather. Over time, a weakened barrier leaves the skin less equipped to defend itself against environmental aggressors and oxidative stress. Repeated exposure to these daily stressors can contribute to chronic low-grade inflammation, often referred to as inflammaging, a process linked to premature skin ageing.

Signs your skin barrier may be compromised

Your skin is often quick to tell you when its barrier needs support. Common signs include:

• Tightness after cleansing or showering

• Persistent dehydration

• Dull or lacklustre skin

• Rough texture

• Increased sensitivity

• Redness

• Flaky patches

• Skincare products that suddenly sting or feel uncomfortable

• Certain skin conditions, including atopic dermatitis, contact dermatitis, psoriasis and ichthyosis, are also associated with increased TEWL²

Why protecting the skin barrier matters

A healthy skin barrier does far more than retain moisture. As aforementioned, it is the skin's first line of defence against UV radiation, pollution, temperature changes and other environmental aggressors. When the barrier becomes compromised, water escapes more rapidly while external irritants penetrate more easily. Supporting the skin barrier therefore minimises excessive TEWL and strengthens its resilience against daily environmental stress. 

Restoring the skin barrier: hydration alone isn't enough

When skin becomes dehydrated, our first instinct is often to add more moisture. While hydration is essential, restoring a compromised skin barrier requires more than simply replacing lost water. Hydration replenishes water within the skin, but a healthy barrier also relies on lipids to prevent that water from escaping. Supporting the skin barrier therefore means combining humectants, which attract water, with replenishing lipids and antioxidant-rich botanicals that help reinforce the skin's natural defences.

Two steps to help minimise TEWL

Reviving Face & Body Mist and Rescuing Body Balm were created to work in synergy, addressing different aspects of transepidermal water loss to help restore and protect the skin barrier. Counteracting TEWL requires two complementary steps: restoring hydration and helping prevent it from evaporating. 

Often described as our serum-in-a-mist, Reviving Face & Body Mist is the first step. It replenishes lost moisture with Rose hydrolat, glycerin and sodium hyaluronate, a low molecular weight form of hyaluronic acid that attracts and binds water to leave skin feeling plumper, smoother and more comfortable. Rich in minerals, amino acids and polysaccharides, algae extract reinforces the skin barrier and improves moisture retention, while wild Indigo and arnica soothe environmentally stressed skin, reducing the visible effects of dehydration and fatigue. Antioxidant-rich botanicals, such as rose and geranium further help defend the skin against the oxidative stress that can accompany prolonged sun exposure, heat and travel.

Once hydration has been restored, Rescuing Body Balm helps lock it in. Rich in replenishing botanical lipids, it reinforces the skin's natural barrier and helps minimise ongoing moisture loss. Babassu oil, naturally abundant in lauric and myristic acids, replenishes essential lipids that help reduce TEWL, while shea butter provides emollient and occlusive support to strengthen the barrier and slow water evaporation. A nourishing blend of botanical oils, including rosehip seed and seabuckthorn oils, restore essential fatty acids to maintain barrier integrity, whereas retinyl acetate supports healthy skin renewal. The formula, rich in antioxidants further offers skin protection from environmental and oxidative stress.

Together, Reviving Face & Body Mist and Rescuing Body Balm address the two essentials of barrier recovery: replenishing water and helping to keep it where it belongs. Whether your skin has been exposed to dry cabin air, summer heat, excess sun exposure or changing climates, this duo tackles excessive TEWL, leaving skin hydrated, strengthened, and balanced all summer long and beyond.

Additional everyday habits to incorporate

Supporting the skin barrier doesn't stop with skincare. A few simple habits can make a noticeable difference throughout the summer.

• Avoid over-cleansing, over-exfoliating or using very hot water.

• Apply moisturiser immediately after bathing while skin is still slightly damp.

• Wear SPF daily to protect against UV-induced barrier damage. 

• Incorporate humectants, replenishing lipids and antioxidant-rich skincare into your routine, while supporting your skin from within with a diet rich in antioxidant-containing foods.

• Stay well hydrated throughout the day.

• Protect skin during air travel with barrier-supportive hydration.

Maintaining skin barrier integrity is fundamental to healthy skin. Beyond simply replacing lost moisture, summer skincare is about protecting the barrier before dehydration takes hold. By combining hydration, replenishing lipids, antioxidant-rich botanicals and barrier-supporting skincare, you can minimise excessive transepidermal water loss (TEWL), strengthen resilience, reduce the effects of environmental stress and maintain vibrant and healthy skin all season long.

¹ https://www.ncbi.nlm.nih.gov/books/NBK513299/

² https://www.sciencedirect.com/science/article/pii/S0022202X18325764