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Adrenaline into the outer thigh, and then keep them lying flat. Standing someone up during anaphylaxis can kill them, and it is the mistake a helpful bystander is most likely to make.

Anaphylaxis is a severe allergic reaction affecting the whole body. It can kill within minutes, and the treatment is a single injection that a frightened bystander can give correctly with no training.

The technique is easy. The part people get wrong is what happens in the two minutes afterwards.

Recognising it

Anaphylaxis, as opposed to an ordinary allergic reaction

An allergic reaction becomes anaphylaxis when it involves airway, breathing or circulation:

System	Signs
Airway	Swelling of the tongue, lips or throat; hoarse voice; difficulty swallowing; a feeling of the throat closing
Breathing	Wheeze, noisy breathing, persistent cough, breathlessness
Circulation	Pale, clammy, dizzy, faint, collapse, drowsiness, confusion

Plus, usually but not always, skin signs: widespread hives, flushing, itching, swelling.

Skin signs can be completely absent. A significant minority of anaphylaxis presents without any rash at all, and waiting for hives before acting is a documented cause of delay. Airway, breathing or circulation involvement is the threshold, with or without a rash.

A sense of impending doom is commonly reported, as it is with sepsis. Take it seriously.

It usually comes on fast, within minutes to an hour of exposure, but it can be delayed by several hours, especially with food.

The sequence

Adrenaline comes first, before the phone call, if you are alone and the device is to hand. It is the only treatment that reverses anaphylaxis, and every minute matters. Antihistamines and inhalers do not treat anaphylaxis and must never delay adrenaline.

Give it even if you are not certain. Adrenaline given unnecessarily to someone who was not in anaphylaxis is very unlikely to cause serious harm. Adrenaline withheld from someone who was, is how people die. The asymmetry is stark and the guidance is unambiguous: if in doubt, give it.

Position, and why it kills

DANGER

Lie them flat on their back with their legs raised. Do not let them stand up, walk, or be helped to their feet. Not to get to the car, not to go to the bathroom, not because they say they feel better.

In anaphylaxis, blood vessels dilate and fluid leaks out of the circulation, so there is not enough volume returning to the heart. Lying flat with the legs raised uses gravity to return blood to the heart and brain.

Standing up removes that return. The heart can be left contracting on an empty chamber, and people have died suddenly at the moment they were stood up or sat up, including after adrenaline had been given and they appeared to be improving. This is a recognised and well-documented cause of death in anaphylaxis.

Exceptions, both of which still avoid standing:

If they cannot breathe lying flat, let them sit up, but keep them sitting on the floor with their back supported, never standing.
If they are unconscious and breathing, put them in the recovery position on the floor.
If they are pregnant, lie them on their left side.

The instruction that matters most on this page is the simplest: once they are down, they stay down, until professional help arrives and says otherwise.

This is the mistake a helpful person makes. Somebody is unwell, so you help them up and walk them to a chair or a car. In anaphylaxis, that specific act of kindness can be fatal.

Using the injector

The devices differ slightly, so read the label on the actual device before an emergency, ideally today. Most now have spoken instructions when you activate them.

The common principle:

Take off the safety cap.
Hold it firmly in your fist, with the injecting end pointing at the outer thigh.
Place it against the middle of the outer thigh, halfway between hip and knee, on the outer side.
Push firmly until it clicks or activates.
Hold it in place for the number of seconds the device specifies, commonly 3 to 10. Count out loud. Removing it early means a partial dose.
Remove and massage the site for about ten seconds.
Note the time.
Keep the used device to hand over to the ambulance crew.

Through clothing is fine. Do not waste time undressing anyone. Avoid seams, thick pockets and anything in the pocket.

Outer thigh only. Not the buttock, not the arm, not anywhere else. The thigh muscle has the blood supply that gets adrenaline working fastest.

The second dose

Biphasic reactions are the reason this matters after apparent recovery. In a proportion of cases, symptoms settle and then return hours later, sometimes up to 12 hours afterwards, without any further exposure. That is why anyone who has had anaphylaxis needs hospital observation even if they seem completely fine, and why "they're better now" is not the end of the episode.

Afterwards

Hospital assessment is required, every time, even after full recovery. This is the biphasic risk above.
Take the used devices and any remaining ones.
Note what they ate, touched or were stung by, and when. This matters for the allergy work-up.
Replace the used devices immediately. Someone with a known allergy and no in-date adrenaline is in a dangerous position, and prescriptions take time.

Storing adrenaline

Worth its own section, because in the scenario this app covers, storage conditions stop being controlled.

Room temperature, 15 to 25°C. Do not refrigerate and do not let it freeze. Freezing destroys it.
Keep it out of direct sunlight and heat. A car glovebox in summer, or on a sunny windowsill, degrades it.
Check the window. The liquid should be clear and colourless. Discolouration, cloudiness or visible particles mean discard it.
Check expiry dates monthly and diarise replacements. Auto-injectors have short shelf lives, typically 12 to 18 months.
An expired device is better than nothing in a genuine emergency: potency declines but does not vanish. Use it, then use a second, and say so to the ambulance crew. This applies only when there is no in-date alternative.
Keep them where they can be found in the dark, by someone who is panicking, and make sure everyone in the household knows where.