When avoidance fails
Even with careful label reading, good restaurant communication and sensible cross-contact precautions, accidental exposures can happen.
That raises the part of food allergy nobody particularly enjoys discussing but everybody managing a potentially serious allergy needs to understand:
What does an allergic reaction actually look like — and when does it become an emergency?
The answer is more complicated than "look for swelling".
Skin symptoms can occur.
Gut symptoms can occur.
Breathing can be affected.
Circulation can be affected.
And, importantly, a severe reaction does not have to produce every one of those things.
When an allergic reaction becomes an emergency
Not every reaction to mustard is anaphylaxis.
But one of the difficulties with food allergy is that a reaction can begin with symptoms that seem relatively ordinary and then develop into something much more serious.
A person might notice itching.
Their lips might tingle.
Hives may appear.
They may feel sick or develop abdominal pain.
For many reactions, symptoms remain relatively mild.
Anaphylaxis is different.
It is a serious systemic allergic reaction that can develop rapidly and become life-threatening.
And there is a particularly important misconception to remove immediately:
Anaphylaxis does not have to involve a dramatic rash.
Someone can be experiencing a dangerous allergic reaction without being covered in hives.
That matters because people naturally look for visible evidence. A swollen face looks alarming. A rash covering someone's body looks alarming.
A dangerous fall in blood pressure may be almost invisible.
Think airway, breathing and circulation
A useful way of recognising the dangerous features of an allergic reaction is to think about three fundamental systems:
Airway. Breathing. Circulation.
The airway is the route through which air reaches the lungs.
An allergic reaction can cause swelling involving structures such as the tongue or throat. Someone may describe their throat as tight, have difficulty swallowing or develop noisy breathing because the upper airway is becoming narrowed.
Breathing concerns what is happening further down.
The lower airways can narrow, causing wheezing, coughing, chest tightness or difficulty breathing.
Then there is circulation.
During anaphylaxis, blood vessels can widen and fluid can move out of the circulation into surrounding tissues. Blood pressure can fall. The brain and other vital organs may consequently receive insufficient blood flow.
Someone may become dizzy, faint, confused, pale, cold or clammy. In the most severe circumstances they can collapse.
Current Resuscitation Council UK guidance emphasises prompt recognition of airway, breathing or circulation problems, which can occur with or without skin or mucosal changes.
That last phrase is worth remembering.
No rash does not mean no anaphylaxis.
Why can the whole body react at once?
Earlier, we described mast cells as containing packets of powerful chemical messengers.
During a major IgE-mediated reaction, activation of these cells can occur throughout the body.
Among the substances released is histamine, but histamine is only part of the story. Other mediators also contribute to inflammation, airway narrowing, changes in blood vessels and other effects.
This helps explain the apparently chaotic collection of symptoms.
The skin may itch because processes are occurring in its blood vessels and tissues.
The lips may swell because fluid is moving into tissues.
The gut can contract and react.
The airways can narrow.
Blood pressure can fall.
These aren't several unrelated illnesses arriving simultaneously.
They are different organs responding to the same systemic event.
Think of a building's fire-alarm system.
One detector activating might trigger bells, unlock doors, close fire doors, stop lifts and alert a control centre.
Those responses look different because different parts of the building are doing different things.
But they have a common trigger.
Anaphylaxis is vastly more biologically complicated than a fire alarm, but the analogy helps explain why a tiny amount of one food can apparently produce symptoms everywhere from the skin to the lungs to the cardiovascular system.
Myth: "No rash means it isn't an allergic emergency"
Again, false.
Skin symptoms are common in allergic reactions.
They are not compulsory.
Someone with dangerous breathing or circulatory problems after likely allergen exposure should not be reassured simply because their skin looks normal.
This is one of those facts worth teaching beyond the allergic community.
Friends, teachers, restaurant staff and relatives often expect allergy to announce itself visibly.
Sometimes the most dangerous part is happening where nobody can see it.