Should I wash a head of lettuce before eating it?

All produce, lettuce included, should be thoroughly washed before eating. This includes home-grown lettuce or lettuce purchased from a grocery store or farmer's market.
 
Washing not only removes any residual dust or soil from lettuce, but also may be helpful in ridding lettuce of harmful bacteria such as E coli. Wash the lettuce in running water just before eating. The water should be cold to maintain crispness. Studies show that washing the lettuce leaf by leaf is the most effective means of reducing bacteria to acceptable levels.
 
Cutting boards, knives and other items used to cut lettuce should be thoroughly washed with soap and warm water both before and after use. Also, wash your hands with soap and warm water after handling lettuce.
 
Source(s):
Environment, Health and Safety Online "Food Safety-Vegetables"
FDA "Safe Handling of Raw Produce and Fresh-Squeezed Fruit and Vegetable Juices"