More people are developing allergies because their immune systems are not exposed to “good dirt”, according to Trinity Professor Luke O’Neill.
Immunology expert Prof O’Neill was asked to break down the science of allergies, something that has seemingly become more common in recent years.
“The big question is allergies are going up,” he said on Show Me the Science.
“More and more people and children are getting allergies and ending up in their GPs with asthma, with eczema with atopic dermatitis or allergic to things in the environment.”
While there is no absolute cause for an increase in allergies, Prof O’Neill said a lot of evidence supports the ‘hygiene hypothesis’.
“When you're a baby and a child, if you live on a farm, for instance, you see lower incidence of allergies,” he said.
“A little bit of dirt – I'm talking about good dirt, not nasty dirt – the dirt is training your immune system not to go out of control.
“If you don't get exposed to dirt as a child, the immune system then starts misbehaving because it hasn't been educated.”
With more people living in urban settings and more parents focused on strict hygiene, allergies become more common.
Prof O’Neill said having a tapeworm can also reduce allergies.
“Many people in Africa are carrying parasitic worms and they rarely get allergies because the immune system is recognising the tapeworm and then is able to behave itself,” he said.
“The parasite is training the immune system not to overreact to things.
“In ancient times, we were all carrying these parasites because that was a natural order of things.
“Then of course, in the 20th century, we kill the parasites, and now we live in an environment that's far too clean.”
The cause of allergies themselves is also somewhat of a mystery, according to Prof O’Neill.
“One of the big reasons is genetics,” he said.
“Identical twins have the exact same genes - if one of them has an allergic reaction, there's a 70% chance that the other one would as well.
“Non-identical twins, if one has an allergy there's a 40% chance.
“That's a very interesting difference there, because that tells us the genes are pretty important.”