Why is my eczema worse in winter? The evidence is strong — and the fixes mostly aren't

The winter problem nobody writes about: you're too warm, not too cold

Every winter eczema article opens with dry air and central heating. Mine opens on a tram.

You're wearing a coat over a hoodie over a t-shirt because it's minus five outside. The tram is heated to roughly the temperature of a sauna. You're sweating under three layers, you can feel it, and you know exactly what it means: tonight is going to be bad. There's nothing to do about it — you're twenty minutes from your stop.

Then you get where you're going, into an overheated room, and everyone else takes their sweater off.

And here's the part I've never seen written down anywhere. Sometimes I keep the sweater on. Not because I'm cold — I'm roasting. Because of what's under it. Because the skin on my arms is not something I want to explain to a room of people, and putting up with the heat is easier than the look someone gives you and then pretends they didn't.

So the thing that's actively damaging my skin — heat and sweat trapped against it — gets prolonged by the embarrassment about how that skin looks. The problem sustains itself. If you have eczema you probably didn't need me to explain that loop, and if you don't, that loop is most of what living with this is like.

The rest of winter is more predictable: the cold itself dries you out, skin cracks, and if you skip moisturising even for a day or two you pay for it. But the layers are what I'd fix first if I could only fix one thing.

What surprised me is that the research agrees with me — and that this is the part of winter advice with actual measured data behind it, while the parts everyone repeats have almost none.

Is eczema really worse in winter, or does it just feel that way?

It's real, and this is unusually well documented. Unlike shower temperature, where I found no controlled study at all, seasonality shows up consistently across countries, study designs and outcomes:

• Denmark, national registries over 156 months: for every 1 °C drop in monthly temperature there were about 2 more clinic visits, 18 more topical steroid prescriptions and 53 more calcineurin-inhibitor prescriptions (Hamann 2018).
• Finland, Helsinki primary care, ~2,750 patients a year: visits peak in January, February, March and November, and bottom out in July (Räisänen 2025).
• China, 10,747 hospital visits over six years: risk climbs below about 19.6 °C, and below freezing the relative risk was 2.6 — with the effect lasting seven to eight days after the cold (Chen 2023).
• 42 countries, twenty years of Google searches: “eczema” and “atopic dermatitis” peak January through May (Maazi 2024).
• A 2025 systematic review of 42 studies across 14 countries graded it: low temperatures in cold climates probably increase eczema visits (Park 2025, JAMA Dermatology).

There's even a hint that it's not purely the outdoor cold. The one study that separated heating from temperature found that “heating degree days” — roughly, how much a region heats its buildings — independently predicted eczema prevalence in a survey of 91,642 children (Silverberg 2013). Not proof that radiators are the culprit, but the closest thing that exists.

Why cold air dries out eczema skin: the filaggrin story

This is the most satisfying mechanism I've come across writing these articles, because it's not hand-waving — it's measurable physics happening in your skin.

Your skin makes its own moisturiser. A protein called filaggrin gets broken down into free amino acids that hold water in the outer layer; dermatologists call the result “natural moisturising factor”. People with eczema often have less of it to begin with.

Here's the part that matters for winter: that breakdown is controlled by the humidity of the air. In the original 1986 work, filaggrin proteolysis ran only between roughly 80% and 95% relative humidity, and stopped outside that window (Scott & Harding). In a human reconstructed-skin model, dropping the air to 30–50% relative humidity — which is exactly what your flat is in January with the heating on — dramatically accelerated the chemical modification that makes filaggrin fall apart faster (Cau 2017).

And sudden change may be worse than steady dryness. Moving mice from above 80% humidity to below 10% made water loss through the skin jump six- to sevenfold within two days (Sato 2002). Which is a decent description of a winter day: minus five outside, twenty-three degrees and bone-dry inside, and you cross between them six times.

Two honest caveats. All of this is animal work and lab models — nobody has run it on people with eczema in their actual homes. And there's a paradox the marketing never mentions: in mice, sustained dry air eventually made the barrier thicker and more resistant, not weaker. The story is real, but it isn't finished.

The best-evidenced winter advice is the one nobody gives: don't overheat

Now the part that matches my tram.

A study followed 60 children with daily electronic diaries for up to nine months and calculated how strongly each exposure tracked with flares. The list, strongest first: house dust 0.53, sweating 0.24, nylon clothing 0.23, other people's pets 0.22, shampoo 0.07 (Langan 2009).

Sweating came second. Ahead of pets. Ahead of shampoo. And nylon clothing was right behind it.

There's a mechanism, and it's a cruel one: in atopic skin, sweating itself is impaired, so heat gets retained rather than shed — and retained heat drives itch, which builds through the evening (Murota & Katayama 2017).

Put those together and the practical winter advice writes itself: “don't overheat” is probably a better winter rule than “don't wear wool” — and it's the one you'll never see on a leaflet, because nobody sells anything for it. Layers you can actually take off in a warm room beat one thick jumper you're stuck in. Which brings me back to that room where I keep the sweater on, and to the honest admission that knowing this doesn't always make me take it off.

Is wool bad for eczema? It's microns, not materials

The standard patient-leaflet line is “never wool, always cotton”. That turns out to be the wrong distinction.

A 2017 review put it bluntly in its title — Debunking the Myth of Wool Allergy (Zallmann 2017). No wool allergen has ever been identified, and there's no specific IgE to it. The itch is mechanical: fibres thicker than about 30–32 microns are stiff enough to press on the skin and set off the nerve endings that signal itch — and that's true regardless of what the fibre is made of. A coarse synthetic prickles the same way. Superfine merino runs 15–18.5 microns; ultrafine is finer still.

So it isn't natural versus synthetic. It's thick versus thin.

There are even randomised trials of superfine merino in eczema — which makes clothing, oddly, the one winter intervention with proper trial evidence. A crossover trial in 39 young children found meaningfully lower severity on merino than cotton after six weeks and roughly half the topical steroid use (Su 2017); a second in 50 people found better severity and quality-of-life scores (Fowler 2019).

The caveat you must know before buying anything: two of the three merino studies were funded by Australian Wool Innovation, the total across all of them is about 120 people, and nobody independent has replicated it since. That's simultaneously the best and the weakest evidence in this whole article.

Meanwhile, the fabrics with the biggest trials both lost. Silk clothing was tested in 300 children over six months and produced no benefit at all, at a modelled cost of £56,811 per quality-adjusted life year (CLOTHES trial, 2017). Antibacterial clothing — silver and chitosan — was tested in 171 people over a full year and made no difference to severity, quality of life, steroid use or bacteria on the skin (ABC trial, 2024).

Do humidifiers help eczema?

This is the big one, so let me be exact about what I looked for and didn't find.

Searching the medical literature for any intervention study of a humidifier in eczema returns nothing. Searching the clinical trials registry for humidifier trials in any skin condition returns zero. Cochrane has a review on dust-mite measures and none on air humidity. And none of the major guidelines — American, European, Japanese — make a graded recommendation about humidifiers at all.

That's remarkable for a device this widely recommended. The mechanism above is genuinely better than most things sold for eczema, and the market still ran decades ahead of the evidence.

What actually exists instead:

• The best controlled experiment on record is from 1992, in a Helsinki office building: 290 office workers, humidified wing versus dry wing, and dryness symptoms scored significantly lower with humidification (Reinikainen 1992). Office workers, not eczema patients, and a symptom questionnaire, not a severity score.
• A 2022 study humidifying rooms to 40% and 50% found improved skin hydration but no effect on water loss through the skin, in healthy people.

And there's counter-evidence that ought to give any humidifier ad pause. The largest US eczema cohort — 5,595 children followed for eight years — found that warmer, more humid and sunnier climates were associated with worse-controlled eczema, not better (Sargen 2014). The 2025 JAMA Dermatology meta-analysis reached the same direction: higher humidity is probably associated with increased severity, at moderate certainty.

Both things can be true. “Humid” in Singapore and “humid” in a Czech panel flat in January are not the same variable. Which is exactly why the general rule fails and your own log doesn't.

One more thing worth knowing: that 40–60% humidity range you see everywhere isn't an eczema treatment target. It's the range where you avoid mould at the top and static electricity and dryness complaints at the bottom. The engineering standard for thermal comfort doesn't set a lower humidity limit at all. The eczema charities that quote 40–60% are giving sensible household advice, not citing a trial.

If you do run one, two proportionate cautions rather than scare stories. Dust mites do better as humidity climbs — pushing your flat to 60% “for your skin” also makes it pleasant for them. And a contaminated tank can cause a rare lung condition that has been documented since 1970, so clean it and put nothing in the water but water.

Should you switch to a thicker ointment for winter?

Very reasonable-sounding, and it has been tested once — indirectly, and it came out null.

A trial of 550 children across 77 practices compared lotions, creams, gels and ointments head to head. No difference in severity between them (p = 0.77). Ointments did sting less. And in a secondary analysis, the type of emollient did not change the relationship between cold weather and flares at all (p = 0.55) (BEE trial).

So: moisturising in winter, yes, absolutely — emollients are the single best-evidenced thing in eczema care, cutting flare risk substantially across 77 trials. Ceremonially switching to the thick winter tub in October: no evidence that this specifically helps. Use whichever one you'll actually apply, because the one you use beats the one that's correct.

What about vitamin D in winter?

Winter is the vitamin D deficiency season, so this ought to work. The evidence is thinner than the enthusiasm.

Two winter trials exist. In Ulaanbaatar, 107 children whose eczema worsened in winter took 1,000 IU a day for a month and did modestly better than placebo (Camargo 2014). The other, in Boston, had eleven participants (Sidbury 2008). Both ran for just one month, and the larger of the two never measured anyone's baseline vitamin D level to begin with.

That's a hypothesis worth taking seriously, not a settled answer — and dosing is a conversation for your doctor, not a blog.

The one thing winter does right

Not everything about winter is worse, and this is my own honest observation: I sleep better in winter. The bedroom isn't stiflingly warm, and I fall asleep more easily.

That may be more useful than it sounds. Night-time itch has a documented physiology — skin temperature rises in the evening, water loss through the skin climbs overnight, and your natural cortisol is at its lowest (Patel 2007). Since retained heat drives itch, a cooler bedroom is a plausible free intervention, and the one winter change that costs nothing. Nobody has tested bedroom temperature in eczema either — I'll be writing about night-time itch properly soon.

Not everyone is a “winter type”

Before you rearrange your life around any of this: a survey of 11,585 children found four different seasonal patterns, not one. Some flare in spring, some in summer and autumn, some in winter, and some show no clear weather link at all (Yang 2026).

So “eczema gets worse in winter” is true of populations and may simply not be true of you. Mine is a winter one. A friend's is emphatically not.

How to find out what winter actually does to your skin

The research can tell you what happens on average across thousands of people. It can't tell you which of the four patterns you are, whether your problem is the dry air or the jumper, or whether that humidifier is doing anything.

But winter hands you an unusually good natural experiment, because the variables change hard and fast. Pick one — the layers you wear indoors, the bedroom temperature, a humidifier if you already own one — and log your skin daily (intensity and itch, 1 to 10) alongside it for two weeks. Then look at whether they line up. Your memory will tell you “winter is bad” and stop there; a daily log tells you which part of winter.

If I had to bet on where most people's winter answer is hiding, it's not the humidifier. It's the sweating. That's the one with measured data behind it, and it's the one nobody thinks to log.

A notes app works fine. I built Exemio because I got tired of doing this by hand, and it surfaces the correlations for me — but the method matters more than the tool. If you want a head start on which variable to test first, my 2-minute trigger check is where I'd begin.

iPhone · iOS 16+

Common questions

Sources

1. 1. Hamann 2018 — season, weather and eczema healthcare use, Danish national registries
2. 2. Räisänen 2025 — seasonal variation of atopic dermatitis burden in Finnish primary care
3. 3. Chen 2023 — ambient temperature and atopic dermatitis visits (10,747 visits, 6 years)
4. 4. Maazi 2024 — seasonal fluctuations in atopic dermatitis, search data across 42 countries
5. 5. Park 2025 — climate conditions, weather changes and atopic dermatitis: systematic review and meta-analysis (JAMA Dermatology)
6. 6. Silverberg 2013 — climatic factors and childhood eczema prevalence (n=91,642)
7. 7. Scott & Harding 1986 — filaggrin breakdown to water-binding compounds is humidity-dependent
8. 8. Cau 2017 — lowering relative humidity increases epidermal protein deimination
9. 9. Sato 2002 — abrupt decreases in environmental humidity and skin barrier abnormalities
10. 10. Langan 2009 — what causes flares of eczema in children? (daily diaries, n=60)
11. 11. Murota & Katayama 2017 — exacerbating factors of itch in atopic dermatitis
12. 12. Zallmann 2017 — Debunking the Myth of Wool Allergy
13. 13. Su 2017 — DESSINE trial: superfine merino vs cotton in infantile eczema (n=39)
14. 14. Fowler 2019 — effects of merino wool on atopic dermatitis (n=50)
15. 15. CLOTHES trial 2017 — silk garments for childhood eczema, RCT (n=300)
16. 16. ABC trial 2024 — antibacterial therapeutic clothing, RCT (n=171, 52 weeks)
17. 17. Reinikainen 1992 — air humidification and symptoms in office workers (n=290)
18. 18. Sargen 2014 — warm, humid and high sun exposure climates associated with poorly controlled eczema (PEER, n=5,595)
19. 19. BEE trial 2022 — lotion vs cream vs gel vs ointment emollients for childhood eczema (n=550)
20. 20. Camargo 2014 — vitamin D for winter-related atopic dermatitis, RCT (n=107)
21. 21. Sidbury 2008 — vitamin D for winter-related atopic dermatitis, RCT (n=11)
22. 22. Patel 2007 — nocturnal itch: why do we itch at night?
23. 23. Yang 2026 — distinct seasonal attack patterns of childhood atopic dermatitis (n=11,585)

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