Do I have a lettuce allergy? What are signs?

Possible. Yes, it is possible to have allergy to lettuce, but it is one of the more rare food allergies. Typical symptoms would be mouth itching or soreness, nausea, vomiting, abdominal cramps, diarrhea, hives, itching or rarely in more severe cases trouble breathing, drop in blood pressure (shock), or death. You only need one or two of these symptoms to suspect an allergy.