We think you should be able to see exactly how our forecast is built, including where it is strong and where it is uncertain. This page explains what goes into the EczemaZone flare risk estimate, why each factor is there, what we leave out on purpose, and the honest limits of what weather data can and cannot tell you about eczema.
What the forecast is, and what it is not
Our forecast reads the current and upcoming weather and air quality for a specific location and turns it into a daily flare risk estimate on a simple scale from Low to Severe. It is a way to see when local conditions are likely to be harder on eczema prone skin, so you can prepare.
It is not a diagnosis, and it is not a prediction of what will happen to you personally. Eczema is highly individual. As you will see below, the science supports weather as a real influence on eczema at the population level, but not as a precise day to day predictor for any single person. We report risk, not certainty.
The factors we include, and why
We include only factors that have real scientific support and that we can measure for your location from reliable data. In rough order of how much weight they carry:
Temperature, both cold and hot
Temperature is one of the best supported influences on eczema, and importantly it works in both directions. A 2025 systematic review of dozens of studies found that both temperature extremes are associated with worse eczema. Cold tends to drive the winter pattern many people know, while heat drives a separate summer pattern for others. Because the direction genuinely differs from person to person, our model treats both cold and hot extremes as risk rather than assuming one direction. More on that below.
Dry air (low humidity and dew point)
Dry air is the core of the cold weather pattern. When the air holds little moisture, water leaves the skin faster, which weakens an already compromised barrier and drives itch and flare. We use dew point, which reflects how much moisture the air actually holds, along with relative humidity. Cold and windy conditions make this worse, so they feed into the same factor.
Heat with humidity
At the other extreme, hot and humid conditions are their own problem, because sweat and its salts sit against the skin and irritate it. This factor only activates when it is both hot and humid, since dry heat behaves differently and is captured by the dry air factor instead.
Air pollution
Fine particle and gas pollution measurably worsens eczema. The evidence here is strong and has been repeated across many studies, with airborne particulate matter (including wildfire smoke) among the most consistent findings. We include particulate matter and common gaseous pollutants. Because pollution effects tend to build over days rather than acting the same day, we treat this as a slower moving layer.
Grass pollen
For people whose eczema is linked to allergies, airborne pollen can trigger flares, and this has been shown directly in controlled studies. Because it only affects a subset of people, we treat pollen as a supplementary factor with a smaller weight.
What we deliberately leave out, and why
Being clear about what we exclude is part of being trustworthy.
- Day to day temperature swings. This sounds plausible, but when we tested the specific claim against
the research, it did not hold up. We rely on actual conditions, not how much they changed from yesterday.
- Sun as a benefit. A common belief is that sun helps eczema. The evidence is mixed at best, and one
large study found greater sun exposure associated with worse control. We do not treat sun as helpful for eczema, and we give ultraviolet light only a small, cautious weight.
- Rain. Its effect is weak and mostly acts through humidity, which we already include, so counting it
separately would be double counting.
- Barometric pressure. We found no solid evidence linking air pressure to eczema, so it is not used.
- Hard water. Hard water has a real but weak and uncertain association with eczema, and it is a fixed
property of local plumbing, not something a weather forecast can track day to day. We leave it out of the daily estimate.
Why we treat both cold and hot as risk
The most interesting finding in the research is that eczema does not respond the same way in everyone. Studies have found people split into distinct groups, some whose eczema is worst in the cold, dry winter, and others whose eczema is worst in the hot, humid summer. Two large studies even pointed in opposite directions on temperature, and that is not an error. It reflects real differences between people.
So instead of assuming a single direction, our model runs two opposing seasonal patterns, a cold and dry pattern and a hot and humid pattern, and reports whichever one your local conditions are pushing on today, along with the pollution layer. When you look up your area, the forecast tells you which pattern is driving the risk, so it makes sense for where you live and the time of year.
Why weather affects eczema at all
Underneath all of these factors is one shared mechanism. Eczema prone skin has a weakened barrier that does not hold moisture or block irritants well. Dry air, pollution, and temperature stress all push on that barrier in different ways, increasing water loss and inflammation. Researchers measure this barrier stress in a lab as transepidermal water loss. We cannot measure your skin from a weather station, and that lab measure is itself noisy from person to person, so we use it only to explain why these conditions matter, not as a number in the forecast.
The honest limits
This is the most important section, so we will not bury it.
- It is a population level estimate, not a personal prediction. The factors above raise or lower the
odds of a flare across many people. Your own skin may respond differently on any given day.
- People genuinely differ, sometimes in opposite directions. The same cold, dry day that is hard on one
person can be fine for another whose eczema is a summer condition.
- No weather based eczema forecast has been formally validated against real flare outcomes. We are
transparent that this includes ours. The forecast reflects well supported relationships, but its per person daily accuracy is inherently limited.
- Much of the underlying research comes from outside the United States, often in places with higher
pollution than most US cities. We use that research for the direction and relative importance of each factor, not as exact numbers.
The most useful thing this forecast can do is help you notice, over time, how your own skin responds to the conditions we surface. That personal pattern is worth more than any single day's estimate.
Where the data comes from
- Weather (temperature, humidity, dew point, wind, ultraviolet index): Open-Meteo.
- Air quality (particulate matter and common gaseous pollutants): Open-Meteo Air Quality.
- Pollen: a pollen data source covering the United States.
We refresh these daily for every location we cover.
Sources
The relationships above are drawn from peer reviewed research and dermatology authorities, including a 2025 systematic review and meta analysis of climate, weather, and air pollution in atopic dermatitis (Journal of the American Academy of Dermatology), a 2024 International Eczema Council review of climate and eczema, a US cohort study of childhood eczema control, studies of seasonal eczema subtypes, controlled studies of air pollution and pollen exposure, and guidance from the National Eczema Association and the American Academy of Dermatology. Full source links are listed in our references and were verified before publication.