Why do people have seasonal allergies? - Eleanor Nelsen
Ah, spring.
Grass growing, flowers blooming,
trees growing new leaves,
but if you get allergies,
this explosion of new life probably
inspires more dread than joy.
Step outside, and within minutes,
you're sneezing and congested.
Your nose is running,
your eyes are swollen and watery,
your throat is itchy.
For you and millions of others,
it's seasonal allergy time.
So what's behind this onslaught of mucus?
The answer lies within you.
It's your immune system.
Seasonal allergies, also called hay fever,
or allergic rhinitis,
are a hypersensitive immune response
to something that's not actually harmful.
Pollen from trees and grass,
and mold spores from tiny fungi
find their way into your mucous membranes
and your body attacks
these innocuous travelers
the same way it would infectious bacteria.
The immune system has a memory.
When a foreign substance gets tagged
as threatening,
white blood cells produce
customized antibodies
that will recognize the offender
the next time around.
They then promptly recruit
the body's defense team.
But sometimes, the immune system
accidentally discriminates
against harmless substances,
like pollen.
When it wafts in again, antibodies
on the surface of white blood cells
recognize it and latch on.
This triggers the cell to release
inflammatory chemicals,
like histamine,
which stimulate nerve cells,
and cause blood vessels in the mucous
membranes to swell and leak fluid.
In other words, itchiness, sneezing,
congestion, and a runny nose.
Allergies usually, but not always, show up
for the first time during childhood.
But why do some people get allergies
and others don't?
Allergies tend to run in families,
so genetics may be one culprit.
In fact, errors in a gene that helps
regulate the immune system
are associated
with higher rates of allergies.
The environment
you grow up in matters, too.
Being exposed to an allergen as a baby
makes you less likely to actually develop
an allergy to it.
People who grow up on farms,
in big families,
and in the developing world also tend
to have fewer allergies,
although there are plenty of exceptions,
partly thanks to genetics.
One theory is that as children,
they encounter more of the microbes
and parasites
that co-evolved with traditional
hunter-gatherer societies.
Called the hygiene hypothesis,
the idea is that when the immune system
isn't exposed
to the familiar cast of microbes,
it'll keep itself busy mounting
defenses against harmless substances,
like pollen.
Another theory is that an immune system
toughened up by a barrage of pathogens
is less likely to overreact to allergens.
Pollen is a common offender,
just because we encounter so much of it,
but there's a long list of substances:
dust,
animal dander,
insect venom,
medications,
certain foods,
that can send your immune system
into overdrive.
Some of these reactions can be scary.
An allergy can develop
into full-blown anaphylaxis,
which typically brings on severe swelling,
shortness of breath,
and very low blood pressure.
It can be deadly.
The body can even have
an allergic reaction to itself
causing auto-immune disorders,
like multiple sclerosis, lupus,
and type 1 diabetes.
But even non-life threatening allergy
symptoms can make you miserable,
so what can you do about it?
Medications can help reduce the symptoms.
The most common ones keep histamines
from binding to your cells.
These antihistamines
stop the inflammation response.
Steroids can help dial down
the immune system.
Another more permanent option
is immunotherapy.
Deliberate, controlled exposure
to gradually increasing
amounts of an allergen
can teach the immune system
that it isn't dangerous after all.
And if you're really adventurous,
there's a less traditional option:
intestinal parasites.
When hookworms sink their teeth
into the intestinal wall,
they secrete chemicals
that blunt the immune system.
Some studies suggest that hookworms
can treat allergies,
which may be another reason
allergies are more common
in industrialized countries
where hookworms are few
and far between.
Of course, you can always just wait
your seasonal allergies out.
The spring pollen onslaught dwindles
by mid-summer,
just in time for ragweed season.
