05/10/2026
Anaphylaxis isn't “just an allergy”.
It's Anaphylaxis Awareness Week.
So before we talk about adrenaline pens, allergens and what to do in an emergency, let's start at the beginning.
What actually happens inside your body during anaphylaxis?
Your immune system normally has a very useful job.
It identifies things that could harm you and attacks them.
But with an allergy, it gets something wrong.
It identifies something normally harmless — perhaps a food, medication, insect sting or latex — as a threat.
The immune system can then become sensitised to it and produce antibodies against it.
I tend to think of those antibodies as the body's wanted poster:
We've seen this before. We've decided it's dangerous. If it turns up again, we're ready.
That first exposure may cause no obvious symptoms at all. You may not even know it happened.
But when the allergen is encountered again, those antibodies recognise it and can trigger immune cells to release chemicals, including histamine.
And now the body's defence system can go into full attack mode.
The problem is:
The thing it's attacking may not be dangerous.
The body's response can be.
* Histamine makes your blood vessels widen. That can cause your blood pressure to fall — potentially leading to anaphylactic shock.
* It also makes tiny blood vessels more leaky. Fluid that should be circulating in the bloodstream can escape into the surrounding tissues.
* That contributes even further to the falling blood pressure.
* Elsewhere, that fluid can cause swelling. It can collect between layers of skin, producing the raised, itchy areas we recognise as hives.
It can cause swelling of the lips and face.
And when tissues around the tongue and throat swell, it can threaten the airway.
*Meanwhile, the muscles around the airways can tighten — bronchospasm — causing wheezing and making breathing difficult.
And it doesn't stop neatly at Airway, Breathing and Circulation.
The gut can become involved too, causing abdominal cramps, nausea, vomiting or diarrhoea.
Someone may become dizzy, confused, faint or collapse.
Their skin may become red, itchy or swollen.
Or.....there may be no rash at all.
And here's another important point:
Not everyone knows what they're allergic to.
That frightening reaction may be the first time they realise they have an allergy. Their immune system may have encountered and become sensitised to the allergen previously without them ever knowing it.
Anaphylaxis often develops rapidly, although reactions don't all follow exactly the same pattern or timeline.
So anaphylaxis isn't simply a “bad allergy”.
It's the body's own defence system mounting a potentially life-threatening reaction to something it has decided is dangerous.
And once you understand what's happening inside the body, something else starts to make a lot more sense:
Why does adrenaline work?
We'll get to that later this week.
