A rash of kisses: in some people with food allergies, a smooch can trigger hives and more.

Silly greeting cards often depict a kiss on the cheek of a cartoon figure as a big red imprint of lips. For people with a serious food allergy, real kisses sometimes leave the same mark. But it's not funny. The red wheal signals an allergic hypersensitivity to food residues on the smoocher's mouth. Three new surveys have confirmed what many allergists had been hearing anecdotally--that kisses can trigger allergic reactions.

The most detailed analysis emerges from research at the University of California, Davis School of Medicine. There, during the past 5 years, Suzanne S. Teuber has been surveying people diagnosed with allergies to peanuts, tree nuts, and seeds.

Among 316 patients with especially severe allergies--the type that can induce wheezing and anaphylactic shock--20 had mentioned that they had developed hives or other symptoms after a kiss. Teuber, Rosemary Hallett, and Lori A.D. Haapanen, contacted 17 of the 20 for details, which are summarized in the June 6 New England Journal of Medicine.

In all but one case, the kisser had eaten nuts--sometimes as long as 3 to 6 hours earlier--to which the kissee had a history of being allergic. At least four smoochers had brushed their teeth before kissing. "Many of these were just pecks on the cheek," Teuber says. Symptoms tended to commence within a minute--like the itchy eye and blisters on one mother's eyelid following a brush by her youngster's lips.

Most reactions proved mild, but five kiss recipients developed wheezing or flushing with light-headedness, both potentially dangerous signs. In fact, one 3-year-old had to be rushed to the hospital for treatment of respiratory distress after his mother planted a kiss on his check.

Until now, kiss-triggered hives have been little more than a curiosity. Anne Munoz-Furlong, founder of the Fairfax, Va.-based Food Allergy and Anaphylaxis Network, calls the new UC-Davis study "the first to try to quantify the problem." Its findings, Munoz-Furlong says, indicate that risks from kissing are "a big deal" and give people with food allergy yet another thing to fear.

A KISS GOODBYE? About 2 percent of the U.S. population mounts an exaggerated immunological reaction to certain foods. A few items account for the vast majority of these episodes, with peanuts--a legume--topping the list. Roughly half the persons with food allergies are sensitive to these or tree nuts, such as walnuts, cashews, and almonds. Serious food allergy in this country sends some 30,000 individuals to the hospital each year and kills up to 200, at least three times as many as die from insect stings.

Most people, even physicians, don't appreciate the food-allergy risks posed by exposures other than ingestion. A team at Children's Hospital in Buffalo, N.Y., reported 5 years ago that a 10-year-old boy had had an asthma attack triggered by a whiff of hot dogs containing chicken, a meat to which he was intensely allergic.

People with a severe allergy to peanuts can develop low-grade reactions while aboard planes on which the snack has been given to other passengers, notes Nils E. Eriksson, a retired Swedish food allergist associated with County Hospital in Halmstad.

In the September 2001 Allergy, Brunello Wuthrich of the University Hospital in Zurich reported that a physician allergic to peanuts developed puffy lips and itchiness after a girlfriend's smooch. Knowing of her sweetie's hypersensitivity, the woman--who had eaten a few peanuts 2 hours earlier--had brushed her teeth, rinsed her mouth, and chewed some gum before the kiss.

In the UC-Davis analysis, about 6 percent of the study participants with severe food allergies reported reactions from kissing. However, Teuber told Science News, this is probably an underestimate because we never [initially] asked about kissing"

The Halmstad team did raise the question in a survey of 1,139 Swedes claiming food hypersensitivity. At a symposium last year in Venice, Italy, Eriksson reported that fully 12 percent of the respondents answered "yes" to the question: Do you get symptoms when you are in close contact with--for example, kissing--another person? More recently, his group surveyed 1,100 people with food allergies in Sweden, Denmark, Estonia, Lithuania, and Russia. Again, roughly 12 percent reported reactions from close contact.

The good news is that "a peek on the cheek is unlikely to cause a severe problem," observes Scott Sicherer of the Mt. Sinai School of Medicine's Jaffe Food Allergy Institute in New York. Passionate kisses, however, increase the likelihood and duration of exposure to another's saliva and, "there could be some real danger" he says.

Physicians recommend that people with severe food allergies always carry self-injectable epinephrine. Sicherer says, "It will buy time to get to a hospital emergency room."

Teuber sees another lesson in the data: Those who court romance mustn't be shy about alerting their partners to their allergies.