The condition is usually reported in occupational cases, even though most cases are actually non-occupational and may be partly caused by cross-reactivity.
The researchers recommend patch testing with freshly cut lettuce stem, along with Compositae mix. They also advise carrying out prick-prick tests and potentially, scratch tests. It might be worth remembering that patients whose occupation involves exposure to lettuce, or those who enjoy gardening or keep pets that eat lettuce, may be at risk of the condition.
Paulsen E, Andersen KE. Contact Dermatitis August 19, 2015; doi: 10.1111/cod.12458