Why dry winter air makes you sick – and what your skin has to do with it.

Your skin is more than just a covering – it's your first line of defense. Why dry air from heating systems increases susceptibility to infection and which strategies truly protect you.

Your body has a firewall – and winter is hacking it.

It's almost Christmas. The heating is on full blast in the office, it's 2 degrees Celsius outside, and inside the air feels like the Sahara. Your skin is tight, your lips are chapped, and somewhere in the back of your mind you're wondering: Why do I get sick every winter?

The answer is closer than you think – literally right in front of you. Your skin.

What most people don't know: Your skin isn't simply a passive covering that holds your body together. It's an active immune organ – your first line of defense against viruses, bacteria, and environmental stressors. And it's precisely this system that is systematically weakened during the winter.

The skin as an immune organ: What science says

More than one barrier

Your skin, at approximately 2 square meters, is the largest organ in your body – and one of the most complex. It consists of several layers, each fulfilling a specific protective function:

The stratum corneum (horny layer): The outermost layer consists of dead cells held together by lipids (fats). This structure functions like a brick wall – the cells are the bricks, the lipids the mortar. If the mortar becomes brittle, gaps form.

The acid mantle: Your skin has a slightly acidic pH value (4.5-5.5), which inhibits the growth of pathogenic germs. This natural protective film is formed by sebum and sweat – and is often disrupted in winter.

Immune cells in the skin: Langerhans cells reside in the epidermis – specialized immune cells that recognize pathogens, engulf them, and report them to the adaptive immune system. They are the guardians of your first line of defense.

Research findings from 2024 confirm: The skin is an active part of the immune system, coordinating both innate and acquired immune responses. When this barrier is disrupted, the risk of infection measurably increases.

TEWL: The invisible enemy

Scientists often measure the integrity of the skin barrier using the so-called TEWL value – transepidermal water loss, i.e., the loss of water through the skin. Typical reference ranges, depending on the body region and measurement method, are in the low single-digit to double-digit gram range per square meter per hour.

The problem: In very dry indoor air, this value can increase significantly. A Korean study from 2023 showed that even 6 hours in heated rooms with less than 20% humidity led to measurable changes in skin function – including increased TEWL, reduced hydration, and altered barrier function.

What this means: Your skin loses moisture faster than it can replenish it. The lipid layer becomes more fragile, the pH value can shift, and micro-cracks develop. And it is precisely through these micro-cracks that microorganisms have an easier time than they would with a stable skin barrier.

The urban winter factor: Why city dwellers are particularly affected

City life puts a particular strain on your skin barrier in winter. You're constantly moving between extreme environments: freezing cold outside, overheated rooms inside. These abrupt changes in temperature and humidity put additional stress on your skin.

Heated air: Typical office spaces have a humidity level below 35% in winter – sometimes even below 20%. The ideal range for skin is 40-60%. The deficit is enormous.

Temperature shocks: The constant change between cold outdoor air and warm indoor spaces prevents the skin from adapting to a stable environment. This overwhelms the thermoregulation system.

Air pollution: Fine particulate matter (PM2.5) and nitrogen dioxide (NO2) further increase TEWL. Studies show that all pollutants examined lead to increased transepidermal water loss – the skin barrier is systematically attacked.

Frequent handwashing: Soap and disinfectants attack the skin's protective acid mantle. The COVID pandemic has shown that frequent handwashing with harsh cleaning agents leads to measurable disruption of the skin barrier.

5 Strategies for a Resilient Skin Immune System

1. Optimize humidity

Here's how it works: Invest in a humidifier for your office and bedroom. Target: 40-60% relative humidity. A hygrometer will help with monitoring.

Why this works: Higher humidity reduces TEWL and supports hydration of the stratum corneum. Your skin loses less moisture, the lipid barrier remains more stable, and the pH balance is less disrupted.

Urban Reality Check: A small USB humidifier on the desk can already make a measurable difference – especially in air-conditioned open-plan offices.

2. Prioritize gentle cleaning

Here's how it works: Switch to pH-neutral, soap-free cleansing products. Avoid hot water – lukewarm is perfectly sufficient. Moisturize your hands after every wash.

Why this works: Harsh cleansers and hot water dissolve the skin's natural oils and disrupt the pH balance. Gentle products preserve the skin's protective acid mantle.

Urban Reality Check: A small tube of hand cream in the office, one at home, one in the bag. Consistency trumps product quality.

3. Minimize temperature shocks

Here's how it works: Layered clothing that you can adapt to different temperatures. Gloves and a scarf protect exposed skin. Don't go directly from the outdoors into a hot shower.

Why this works: Every abrupt temperature change is stressful for the skin barrier. Gentler transitions give the skin time to adapt.

Urban Reality Check: Use the waiting time on the subway on the way to work to open your jacket and make the temperature change gentler.

4. Strengthen the skin barrier from within

Certain nutrients support the building and regeneration of the skin barrier from within:

Hyaluronic acid: Can bind 1000 times its weight in water. Taken orally, it supports skin hydration from within. Studies show improvements in skin hydration after just 2-4 weeks at 120mg daily.

Pomegranate extract: Rich in antioxidants (ellagic acid, punicalagin), it protects the skin from oxidative stress caused by environmental factors and supports the natural regeneration of the skin barrier.

Coenzyme Q10: Essential for cellular energy production in skin cells. With increasing age and environmental stress, the body's own Q10 levels decrease – supplementation can support skin regeneration and anti-aging processes.

Astaxanthin: It is one of the more potent natural antioxidants and is being studied in doses of approximately 4–12 mg daily. Human studies have described effects on skin hydration, elasticity, and light-induced skin damage, among other things. The often-cited claim that astaxanthin is "up to 6000 times more potent than vitamin C" refers to laboratory data on antioxidant capacity and cannot be directly extrapolated to humans.

5. Directly support the immune system

While you strengthen the skin barrier, you can simultaneously support the immune system behind it:

Echinacea: Described as immunomodulating, it is traditionally used primarily during cold and flu season. Studies with daily doses of approximately 300–900 mg extract report effects on certain immune markers and on the duration and severity of cold episodes – however, the results are not consistent across all studies.

Elderberry: Provides antioxidant plant compounds and is frequently used to support recovery during cold and flu season. Meta-analyses suggest that standardized elderberry extracts, when taken early, can moderately shorten cold symptoms and duration.

Vitamin D: In winter, levels drop due to lack of sunlight. Vitamin D is essential for the normal function of the immune system; guidelines discuss daily supplement amounts ranging from approximately 800 to 4000 IU, depending on baseline levels, body weight, and region. Ideally, an individual dosage should be determined based on 25(OH)D levels and in consultation with a healthcare professional.

Your first immune system deserves attention

The most important insight: Skincare isn't about vanity – it's part of your immune system care. Every measure that strengthens your skin barrier indirectly supports your defenses against typical winter stresses.

The first step is awareness: your skin is more than just a covering. It's an active protective organ that needs special attention in winter. The second step is action: humidity, gentle cleansing, targeted nutrients – the strategies above aren't rocket science, but they can make a measurable difference.

Your skin fights on the front lines every winter. Time to give it the support it deserves.

Important NOTE

This article is for informational purposes only and does not replace medical advice. If you have any health concerns or are unsure about supplementation, please consult a physician or nutritionist. The effectiveness of dietary supplements may vary from individual to individual.

Sources

GSC Advanced Research and Reviews (2024). “The skin's role in immunity.” 21(03), 444-456.


Kim, J. et al. (2023). “Effects of winter indoor environment on the skin.” Skin Research and Technology.


Green, M. et al. (2022). “TEWL: Environment and Pollution – A Systematic Review.” Skin Health and Disease, 2(2).


Frontiers in Science (2024). “Immune-mediated diseases caused by climate change-associated environmental hazards.”


Proksch, E. et al. (2008). “The skin: an indispensable barrier.” Experimental Dermatology, 17:1063-72.


Continental Hospitals (2024). “How Seasonal Changes Affect Immunity and Raise Infection Risk.”