The Kissing Study
A study was published in 2006 to understand how long peanut allergen stays in the saliva after a person eats. The method was simple: The scientists asked 10 individuals to each eat a peanut butter sandwich. They collected samples of saliva from the participants at different times, including after the participants had rinsed their mouths and brushed their teeth.
The following results were discussed in Food Allergy News (June-July 2006): Immediately after they ate their sandwiches, participants (who rinsed, brushed, or did neither) were all found to have measurable levels of allergen in their mouths. One hour after eating the sandwich, six out of seven participants had undetectable levels of peanut in their mouths. By 4 1/2 hours after the sandwich had been eaten, levels of peanut were undetectable in all participants.
The results of the study gave the scientists confidence that the allergen would become undetectable for the majority of people several hours after they had eaten peanuts or peanut products. The scientists advised people to brush their teeth as well as wait at least a few hours before kissing someone with a peanut allergy.