Hayfever sufferers know all too well the miseries of the late-summer ragweed season: runny nose, sneezing and itchy, watery eyes.

What most don’t know is that among some people allergic to ragweed, common fruits and chamomile can worsen symptoms temporarily. In rare cases, it can cause a life-threatening reaction called anaphylactic shock.

Loretta McConegy, of the Asthma and Allergy Research Center at the University of Medicine and Dentistry of New Jersey, points to the pollen on a ragweed plant. Hayfever sufferers know the miseries of the late-summer allergy season. What most don't know is that among some people allergic to ragweed, common fruits and chamomile can add to the misery and, in rare cases, cause a life-threatening reaction called anaphylactic shock.

That’s because allergy-stimulating proteins in pollens released by plants are chemically similar or even identical to those in some fruits and vegetables, said Dr. Leonard Bielory, director of the Asthma and Allergy Research Center at the University of Medicine and Dentistry of New Jersey.

Ragweed season began in much of the country Aug. 15.

“This is peak season for ragweed or weed pollen,” said Dr. Ronald Weiner, a Lawrence allergy and asthma specialist. “You see a lot of itchy, watery eyes and runny noses, sneezing and increased asthma if they have asthma. It can cramp their style and wreck their day. It can restrict what they can do outside and their enjoyment of life.”

Some people allergic to ragweed feel symptoms spike suddenly after eating honeydew melon, cantaloupe or bananas. Symptoms also can spike after drinking chamomile tea, using soap or face powder containing chamomile, or taking herbal supplements that include it.

This protein cross-reaction, in 1987 dubbed “oral allergy syndrome,” causes itching and tingling of the mouth, lips, throat and even ears, and, in more severe cases, swelling of tissue. Chamomile causes the most severe reactions, occasionally including anaphylactic shock, a severe, often fatal systemic immune reaction.

“The chamomile-ragweed association has been known for a long time, because in the plant kingdom they’re in the same family,” said Bielory, who is teaching doctors about such cross-reactions.

Other foods also can exacerbate ragweed allergies, including cucumber, zucchini and watermelon.

Environmental effects

The number of people suffering from allergies has been rising, surveys find, partly because of pollution and global warming, which has increased levels of carbon dioxide in the air. More carbon dioxide, which plants breathe, dramatically increases the release of pollen, according to some research.

Besides ragweed, mold spores are at very high levels, adding to the misery of many allergy sufferers. The stretch of dry, hot weather with little rain has made mold release its spores well ahead of the usual time, the first cold snap in the fall, Bielory said.

At least 20 percent of Americans suffer from allergies, and ragweed ranks No. 1. There are no firm data on how many people allergic to ragweed suffer cross-reactions from foods during ragweed season, partly because patients often neglect to tell doctors, said Dr. John W. Yunginger, a pediatric allergy specialist retired from the Mayo Clinic. But it’s believed to be a minority of patients.

“We’ve known about some of these (cross-reactions) for over 10 or 15 years,” he said. “What is new is the fact that they’re slowly tracking down the proteins that are involved.”

A shot in the arm

While that research should bring doctors and patients a better understanding of the problem, it’s unlikely to lead to better treatment, Yunginger said.

“It’s popping scientific wheelies,” he said.

In Europe, where doctors have done more research on the issue, some treat patients’ food allergies through immunotherapy using the related plant pollen. In immunotherapy, patients receive weekly shots containing gradually increasing doses of the offending allergen for a year to 18 months to desensitize their immune system. Individual case reports by Yunginger and a few other researchers showed the approach has cured the hayfever and food allergy.

The limited research has not convinced American doctors, and the strategy is rarely used here, said Dr. Donald Pulver, an asthma specialist and assistant professor at the University of Rochester.