Food allergies and eczema in children

By Adem Lewis / in , , /

Once you start looking after patients who’ve
got food allergies, it very quickly becomes apparent that there’s an enormous overlap
with eczema. Most people who have got a food allergy will tell you that during the first
year of life they had eczema. What the studies show us is that the more severe that the eczema
is and the earlier that their eczema starts, the more likely is that they will develop
food allergies. Typically, to things such as egg, peanuts, tree nuts and sesame. As our understanding has developed, it’s now become clear that this isn’t just a coincidence but
actually it’s a causal association. It turns out that skin barrier dysfunction, which is
the leakiness of a skin barrier that you get an eczema actually predisposes to the development
of allergies and the more leaky that your skin is, the more of a chance there is that
the immune system that sits underneath it will see food allergens in the environment
during early infancy typically before the babies started to eat those foods and develop
sensitization to them that then leads to allergy. Eczema is really common. It affects around
20% of UK infants and the majority of children with eczema don’t have any food allergies.
In fact, doing blanket screening for food allergies on all children with eczema, it’s
really unhelpful. It often throws up lots of positive results that actually don’t mean
very much. So, it doesn’t add anything to the care of the child. However, there are
certain children where allergy testing is definitely worth giving further consideration.
For example, those children who have got more severe eczema particularly where the eczema
has proven difficult to treat or eczema that started very early and particularly in children
where it appears to have been a reaction to something. So, for example the first time
the child was given egg, one of the most common food allergies, and there seemed to be some
sort of reaction. It’s children like that where allergy testing particularly when it’s
more focused and it has to be accompanied with a detailed clinical history can be much
more useful. For many years there was debate about what
the underlying cause of eczema was. Some people believe that it was genetic and others believed
that eczema was an allergic disease that was driven by either things in the diet or things
in the environments, and then some years ago those the discovery of the filaggrin gene
which made it much clearer that the underlying problem in eczema is skin barrier dysfunction.
It’s genetically programmed. But that very much predisposes children who have got that
skin barrier dysfunction to get allergies. Those allergies and in childhood it’s typically
food allergies that then contribute to making the eczema worse and that can happen by a
number of different mechanisms. With some children irritant foods with nothing to do with
allergies at all will cause flares of eczema. So classically things like tomatoes or strawberries
will cause redness around the mouth. That’s harmless and nothing to worry about. But with
other children who do have allergies either through an immediate IgE-mediated pathway,
they can cause reactions typically with food such as egg, peanuts, tree nuts, sesame where
there is a very obvious flare of urticaria or angioedema, and associated eczema very quickly
after ingestion, but also there can be delayed type reactions. Type 4 hypersensitivity, where
having foods such as milk or soy in the diet on a regular basis can cause the eczema to
be chronically worse. This is harder to diagnose because it relies on a detailed clinical history
and we don’t have reliable tests to do it, but an exclusion diet can often reveal that
there’s an underlying problem followed by reintroduction to confirm that that food does
make things worse. It’s notoriously difficult to try and work
out if particular foods are causing flare-ups. So really it requires a detailed history together
with allergy testing where it’s appropriate to try to get to the bottom of whether it’s
necessary to do food exclusions. I’m very aware in my practise that many patients will
try and work out exclusions themselves and often not tell their GP for example that they’re
doing these exclusion diets and this can lead to quite significant nutritional issues. So,
it’s really important to engage patients about their concerns, understand what they’re worried
about, what foods they’re nervous about, what they’ve actually excluded and how effectively
they’ve done that. So really this all comes together as a complete package of proper eczema
care that involves getting the first line measures around right, including the emollients,
the topical steroids together with a very open-minded conversation about the possibility
of allergy and then exploring that further if it’s clinically indicated.

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