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.