What Is Causing My Eczema?

One of the most common questions I’m asked in clinic is a very simple one:

“What is causing my eczema?”

It’s a completely reasonable question. If something is triggering a condition, the obvious solution is to identify it and avoid it.

But eczema rarely works that neatly.

In reality, this is one of the most difficult questions to answer in dermatology. There are usually things contributing to eczema, but it’s often extremely hard to pinpoint a single cause. Even within the space of a clinic appointment, drilling down into specific triggers can be challenging.

Part of the reason is that eczema is what we call a complex trait condition. It arises from a combination of genetic predisposition and environmental exposures.

Some of these environmental factors affect almost everyone with eczema. Dry air, for example, tends to worsen eczema because it further dehydrates and weakens an already fragile skin barrier. Weather changes, central heating, and seasonal humidity shifts can all play a role.

Other exposures are much more individual. These include things like pollen, dust mites, skincare products, or particular foods. These factors can be intermittent, overlapping, seasonal, and overall are difficult to idenitfy and measure.

The Allergy Testing Problem

Another common question I hear is:

“Can’t we just do an allergy test to find the cause?”

Unfortunately, it isn’t quite that straightforward.

Eczema is primarily driven by Type IV hypersensitivity, which is a delayed immune reaction. This means that the skin reaction often occurs 48–72 hours after exposure.

Because of this delay, we don’t have simple or reliable allergy tests for most eczema triggers.

The one test that can sometimes help is patch testing, which looks for delayed reactions to substances such as fragrances, preservatives, and metals. Patch testing can be extremely useful in the right patients, but it doesn’t detect everything.

Many people understandably ask about food. However, patch testing does not test for food allergies.

There are other tests, such as skin prick testing, that can identify reactions to things like pollen or dust mites. But these tests detect Type I hypersensitivity, which is an immediate allergic reaction. These allergies are a different immune mechanism from eczema.

People with eczema often do have Type I allergies — hay fever or food allergies are common in the same group of patients. But finding a positive allergy test does not necessarily mean that allergen is driving the eczema.

The Real Challenge: Identifying Patterns

Because there isn’t a reliable single test, much of the detective work comes down to pattern recognition.

In clinic, this usually means asking patients to keep a food and exposure diary.

In theory, this makes sense. In practice, it’s extremely difficult.

Most of us eat multiple foods every day, and eczema flares often occur two to three days after the trigger. Trying to link a flare on Thursday to something eaten on Monday quickly becomes complicated.

On top of this, eczema flares are rarely caused by just one factor. They are often the result of multiple overlapping exposures:

• A drop in humidity

• High pollen levels

• Stress

• A particular food

• Reduced use of moisturisers

• Poor sleep

When several of these happen at once, a flare becomes much more likely.

Trying to untangle this with a handwritten diary is, frankly, very hard.

Should We Even Try to Avoid Triggers?

Interestingly, the Australian eczema guidelines acknowledge this difficulty. They state that there is no strong evidence to recommend trigger avoidance, largely because triggers are so hard to identify and avoid.

I don’t fully agree with this position. We do know that eczema is influenced by environmental exposures and triggers do exist. We are now in an era of personalised medicine, where understanding an individual patient’s triggers should be part of managing the disease.

Avoidance may not always be possible. But anticipating and preparing for flares can still be incredibly useful. For example, if someone knows that their eczema worsens during high pollen periods or in very dry weather, they can step up moisturising or use preventative treatment with sterod creams before the flare really takes hold.

Why I Started Building an App

This challenge — identifying eczema triggers — is something I’ve been thinking about for years.

So recently I decided to try building a solution.

I’ve been developing an app called EczemaTrack. It’s still in its early stages, but the aim is simple: to make trigger tracking easier and more meaningful.

The idea is to allow people to record daily exposures, such as foods, alongside eczema severity and treatments. The app then integrates external data such as:

• humidity

• weather conditions

• pollen counts

By combining these datasets, the goal is to start identifying statistical patterns that might suggest what is contributing to an individual’s flares.

I’ve tried to keep the design as simple and clean as possible, because tracking only works if it’s easy to do every day.

It’s still very early days, but I’ve recently put the app online and we’ve already had around 100 users, along with some encouraging feedback.

I’d Love Your Feedback

Eczema is a condition where patients often become the real experts in their own triggers. My hope is that tools like this might make that process a little easier.

If you live with eczema — or you care for someone who does — I’d love to hear your thoughts.

Is identifying triggers something you struggle with?

Would something like this be helpful?

You can try the early version of EczemaTrack - let me know what you think.

First published on Substack