There are lots of things the body might react to and the Food Standards Agency list 14allergens to look out for in food.
Anaphylactic shock can be fatal within a few minutes if not treated rapidly.
Anaphylaxis can have a rapid onset affecting:
Airway, throat, and tongue can swell up compromising air entry.
Breathing, the tubes inside the lungs can constrict making it difficult to get air out, gas exchange does not occur.
Circulation, Dilated blood vessels can cause a drop in blood pressure, patient may appear dizzy, lightheaded, and confused.
Most people develop and itchy blotchy rash, but not everyone does.
Call 999/112 and state ANAPHYLAXIS
Ask if they have an autoinjector, get it for them and encourage to inject themselves with it. If they cannot do it, follow instructions, and give the injection yourself. Auto-injectors hold adrenaline which once inside the person’s body will shore up their blood pressure and buy them vital time whilst waiting for EMS to arrive.