It usually begins with a ringing or buzzing in Xenia Chan's ear. Then her throat closes, her lips swell, and her breathing becomes increasingly difficult. Sometimes, she blacks out.
"Being allergic to peanuts sucks," says the 22-year-old student, who was diagnosed with a severe form of the allergy at the age of three. "Because of it, I spent too much of my childhood in the emergency room."
In kindergarten, she was told to sit in another room to have her lunch. Growing up, she wasn't allowed to go to her friends' homes because her parents were so afraid she might die. Some children didn't take her allergy seriously, and would intentionally breathe on her after they ate peanut butter.
As an adult, her condition has become less severe - the smell of peanuts no longer sets the allergy off, only ingestion - but she still carries two EpiPens with her. The medical device delivers a measured dose of epinephrine to treat an anaphylactic reaction.
"I've had to be very careful about what I eat," she says. "I was afraid of going into Thai and Vietnamese restaurants for the longest time, and even Chinese food is difficult because it often contains peanut oil."
When told by the Post about a new experimental treatment costing about HK$300,000 that could help her to weather an accidental ingestion of peanuts - and even eat up to 20 peanuts at a go - Chan says she would "do it in a heartbeat".
"I am tired of wondering if the next thing I eat might kill me," she says. "At the same time, though, doctors are optimistic that I might be growing out of my peanut allergy. So I might hold off for another year or so."
Peanut and other allergies are becoming more common, experts say. In Hong Kong, an estimated 4.8 per cent of the population has a food allergy, says June Chan King-chi, senior dietitian at the Hong Kong Sanatorium. The top five allergens are shellfish, eggs, dairy foods, fruits, and peanuts.
In the past, the only treatment for sufferers was avoiding the offending food and managing reactions.
About five years ago, researchers started experimenting with desensitisation - exposing patients to tiny amounts of the allergens until their immune systems don't react to it. However, this process tends to take a long time and patients suffer frequent allergic reactions, some of them severe. Many patients do not complete the treatment.
A study by Cambridge University Hospitals, published in January in The Lancet, put 99 child patients through a six-month oral desensitisation process. After the therapy, 54 to 62 per cent of the children could tolerate the equivalent of 10 peanuts. Four in five subjects reported side effects, such as an itchy mouth (81 per cent) and abdominal pain (57 per cent). About one in four had severe reactions, including wheezing (22 per cent) and a swelling throat (1 per cent).
Scientists recently took a big step forward in helping sufferers using a drug intended for allergic asthma.
In several studies on patients allergic to milk or peanuts, injections of the drug omalizumab in tandem with the desensitisation treatment enabled patients to build up resistance more quickly and with fewer allergic reactions than through a desensitisation process alone.
Food allergies occur when a person's immune system mistakenly reacts to a particular food and produces IgE antibodies that trigger an allergic reaction. Omalizumab attaches itself to these antibodies, preventing them from triggering an allergic reaction.
Last month, the Hong Kong Sanatorium & Hospital's allergy centre announced results of a pilot study involving four children with moderate to severe peanut allergy that showed the approach increased peanut tolerance.
After six months of treatment last year, all the patients went from having a severe allergic reaction after eating a trace of peanut to being capable of eating the equivalent of 11 to 20 peanuts. The treatments were funded by the hospital.
A similar study by researchers at Boston Children's Hospital/Harvard Medical School in the US, published last December in the Journal of Allergy & Clinical Immunology, produced some equally encouraging results.
Of 13 children with a severe peanut allergy - who couldn't tolerate even a quarter of a peanut to begin with - 12 were able to consume up to 20 peanuts a day without receiving any additional medication at the end of the year-long study. In 2009, the Harvard researchers conducted the first study using the omalizumab-desensitisation dual treatment approach - on children with milk allergies. By the end of the trial, nine of the 11 subjects were able to ingest the equivalent of 235ml of milk or more per day. "It was pleasing to have our results confirmed by an independent centre in the US," says Professor Lee Tak-hong, director of Sanatorium's allergy centre. "We are now considering running a larger collaborative follow-on study in Hong Kong."
One of Lee's patients, eight-year-old Tiffany Tsang, can now eat at least nine peanuts daily. Her parents say the family is at last able to dine out with peace of mind.
"In the past, my classmates would give me candy but I could not eat it because I didn't know if it contained peanuts. I was so upset," says Tiffany. "Thanks to the treatment, I'm able to eat candy, ice cream and snacks that contain peanuts."
In the first 18 weeks of the treatment, Tiffany and the other patients in Lee's study were injected once or twice a month with omalizumab.
From week 12 to 26, patients began oral desensitisation by ingesting daily doses of peanut that were gradually increased to the equivalent of nine peanuts. One patient developed mild stomach pain, but Lee says the symptoms resolved rapidly without any extra treatment.
At a food challenge at week 26, the patients were able to ingest 11 to 20 peanuts at a go.
The patients are now going through the three-year-long maintenance phase, whereby they eat nine peanuts daily. When this period is over, patients will stop eating peanuts and will be reviewed for a further three years to ensure long-term tolerance.
Researchers at Stanford School of Medicine and Lucile Packard Children's Hospital Stanford have been testing the ability of omalizumab to accelerate the desensitisation process to not one, but several food allergies at the same time.
In the study published online in February in the journal Allergy, Asthma & Clinical Immunology, the researchers found that patients who took the drug became desensitised to multiple food allergens at a median of 18 weeks, compared to 85 weeks for those who did not take the drug. Many of the study subjects - 50 children and adults in total - had more than five food allergies, the maximum number treated.
But the lead author of the Stanford study, Dr Philippe Bégin, notes - as do Lee, and the Harvard researchers - that so far, the trials have been just pilot studies or phase one safety trials. Further testing in randomised, blind, controlled phase two studies are needed before the dual treatment approach is ready for widespread use.
In the meantime, pregnant women can give their child a head start by eating more nuts during pregnancy. Mothers - who are not allergic to peanuts or tree nuts - and who consume nuts five times a week or more have children with the lowest risk of nut allergy, according to a study published in JAMA Pediatrics in December last year.
"Our study supports the hypothesis that early allergen exposure increases the likelihood of tolerance and thereby lowers the risk of childhood food allergy," say the researchers from the Dana-Farber Children's Cancer Centre in Boston, US. "Additional prospective studies are needed to replicate this finding."