Eczema and asthma are linked.

Because atopic dermatitis is typically the first of the “atopic” diseases to present itself, many people may think that eczema causes asthma. However, this is not likely the case. 

Eczema and asthma are closely related, however, and early eczema is definitely a marker for asthma. In general, infants with eczema are significantly more likely to develop asthma than unaffected infants. About 30% of babies with eczema go on to develop asthma, and up to 80% of kids with eczema get hay fever or asthma later in childhood.

The link between atopic dermatitis and asthma depends on how severe the atopic dermatitis is. 20% of children with mild eczema develop asthma, but more than 60% of children with severe eczema develop asthma. Eczema is also associated with worse asthma severity, and greater asthma persistence into adulthood. 

Doctors have also studied whether “preventing” eczema with probiotics can stop someone from developing asthma, but there is no conclusive evidence of this. In one clinical study, pimecrolimus, a probiotic, was given to one group and a placebo to the other. There was no significant difference in outcomes between the two groups.


Where Eczema Fits In in the Atopic March

Atopic dermatitis is the first of the allergic diseases to present itself. The next disease is typically food allergies, followed by asthma, then allergic rhinitis.

Graph of the atopic march showing the progression of allergic diseases

The progression of allergic diseases, known as the Atopic March.

Eczema is a strong predictor of other allergic diseases. Babies with cracked skin that is missing filaggrin who ALSO have an overactive immune system (high Th2 cells) commonly develop asthma, whereas babies missing filaggrin but a calm immune system (more T regulator cells) do not develop asthma

Doctors believe that atopic dermatitis predisposes babies to asthma when two things happen:

  1. Asthma triggers get through breaks in the skin 
  2. The body has a large number of roving Th2 cells 

When both these things are true, the Th2 cells lock-on to the triggers, even though the triggers are harmless, and attack each time those triggers are breathed into the lungs or enter the sinuses.

We know that genetics play some role in these diseases, but the environment has a larger effect. However, which specific environmental factors (early exposure to things OR lack of exposure to things) set off this march are unknown.


Asthma and Hay Fever: What’s the Difference

The medical term for hay fever is allergic rhinitis. Allergic rhinitis and hay fever are what most people think of when talking about regular, seasonal allergies. 

The common symptoms of someone with hay fever are red, itchy eyes, watery eyes, nasal congestion, and sneezing. Asthma, on the other hand is typified by difficulty breathing. 

In both asthma and hay fever, exposure to an allergen triggers an allergic reaction (meaning histamine is involved). In allergic rhinitis, this reaction happen in the sinuses, whereas in asthma, the reaction causes spasms in the lungs. Hay fever causes so much mucus that it causes wheezing in the airways, but asthma is a reaction that starts in the airways.