An elderly woman who suffered a severe allergic reaction after being stung by a wasp is recovering in Auckland Hospital.

The 71-year-old was flown from Warkworth in a critical condition yesterday afternoon after going into anaphylactic shock.

Auckland Westpac Rescue Helicopter paramedic Ross Aitken said the woman was initially treated by ambulance staff.

When the helicopter arrived, she was conscious but her airway had become very swollen, he said.

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It was not known what type of wasp had stung the woman.

Dr Vincent Crump of the Auckland Allergy Clinic said the elderly were more likely than younger people to suffer severe life-threatening allergic reactions.

"Most people at that age probably have a cardiovascular disease, and they're likely to be on some medication for blood pressure or heart disease. Some of those medications will make a sting anaphylaxis more severe or make it harder to treat."

It was also more common for people to suffer anaphylaxis as they grew older, due to previous exposure to allergens, he said.

"If you've been stung two or three times in close enough succession, the third sting could be the cause of a life-threatening reaction."

It usually took several doses of the venom to trigger anaphylaxis because a certain amount of allergic antibody - built up in response to exposure - was required for the reaction to be severe, Dr Crump said.

Often people weren't aware of what they were allergic to before a severe reaction, he said.

Treatment of anaphylaxis could also be tricky, especially for elderly patients.

An acute asthmatic attack or a heat attack can present just like anaphylaxis, Dr Crump added.

"The treatment for a heart attack is exactly, in some cases, the opposite treatment of what you want to give for anaphylaxis.

"The treatment you want to give for anaphylaxis is adrenaline. For somebody not known to have an allergy, that's [anaphylactic shock] not the first thing you're going to think of if you see an elderly lady collapsed on the side of the road."

Those who were aware of their allergies should carry an Epipen or be desensitised through a series of injections to minimise the risk of suffering anaphylaxis, Dr Crump advised.

A spokesman from the Auckland District Health Board said today the 71-year-old woman was in a stable condition.

The incident followed the near-death experience of a 36-year-old earlier this month who fell unconscious after being stung by a bee.

Jared Cropp was helping his father Joe collect honey from hives near Rotorua when he was stung.

His father was forced to call 111 for help from a motel, after his son's condition deteriorated rapidly on their way back.