For Jennifer Heimall, that otherwise innocent-looking almond cookie on the holiday party tray was the clincher.
A few months before, there was a hint. Heimall, pregnant with her firstborn, Max, felt an unexplained throat tickle. Something she ate?
But after the holiday cookie, and the subsequent throat tightness and hives, there was little room for wonder.
An allergic reaction — in her case, to tree nuts.
Would the specter of food intolerance relegate Max — and his brothers-to-come — to a future of allergen avoidance? Nah.
Heimall, an attending physician with Children's Hospital of Philadelphia's Division of Allergy and Immunology Services, knew better.
Increasingly, research shows that early introduction of some of the most common allergy-provoking foods may be parents' bet best for helping their children avoid developing allergies in the future.
The strongest evidence for early introduction has been for peanuts and eggs, two of the most ubiquitous and frequently allergy-causing foods.
A recent article in the Journal of the American Medical Association looked at data from 146 allergy studies involving more than 200,000 children.
That analysis by researchers at Imperial College London, done at the request of the United Kingdom Food Standards Agency, found that feeding children small samples of peanut butter between the ages of 4 and 11 months reduced the risk of peanut allergy.
Babies fed eggs between ages 4 and 6 months also had a much lower incidence of allergy later in life.
Robert Boyle, lead author of the London analysis, said there have been fewer studies involving other common allergy-provoking foods like cow's milk, fish, sesame, and tree nuts. But he said he thinks early feeding is worth trying for those other foods as well.
"My opinion is that it is reasonable to assume that the same holds true for these other food allergens — that early introduction is likely to be better than delayed introduction until such time as we get evidence to the contrary," said Boyle, whose study results were published in JAMA in September.
He noted that early introduction of gluten-containing foods does not seem to work for preventing celiac disease.
There are good reasons beyond avoiding a childhood without PB&J to try early introduction. Allergy prevention can be lifesaving.
"Unless you've seen a person with a serious allergic reaction," said Joanna Johnson, an allergist with St. Christopher's Hospital for Children, "you can't imagine the severity of it."
Most doctors encourage a commonsense approach to introducing the foods. If there's no family history of allergies, many physicians try the highly allergic food one at a time starting around age 4 to 6 months.
Even with a family history of food allergies, a small taste of the food in question can be tried, but only one at a time should be sampled — don't try peanuts on one day and eggs the next, said Magee DeFelice, an allergist with Nemours/Alfred I. duPont Hospital for Children
The theories about feeding high-allergy foods have evolved over time. About 16 years ago, parents were told to avoid these foods until after infancy.
Several years later, a now-famous study found that Jewish children in the United Kingdom had a much higher rate of peanut allergies than Jewish children in Israel. It turned out, the Israeli children ate peanut-containing food much younger than the British kids; Bamba, a popular puffed-corn-and-peanut treat, was commonly given to Israeli babies.
A later British study, Learning Early About Peanut Allergy (LEAP), showed that peanut consumption starting in infancy and continued through 5 years of age led to an 81 percent reduction in the rate of peanut allergy for high-risk children.
Jonathan Spergel, chief of CHOP's allergy section, said there is no research that supports waiting to offer allergy-linked foods.
"It's pretty consistent that early in food is better," Spergel said.
How to introduce "depends on how nervous the family is," Spergel said.
A very skittish family, he said, could even consider feeding the worrisome food in a pediatrician's office.
Jennifer Heimall tried peanut in the form of Bamba — she found the snack in the kosher section of her supermarket — when her oldest was about 6 months. It's gone well for her two other boys, too.
And when her patients' parents ask if they should start their babies young, she can speak from experience.
"I feel I can say it with confidence," Heimall said. "I would do it, because I have."