According to your question, I think you are worried about eating raw lettuce because of its hygiene. In fact, lettuce, like cucumbers and tomatoes, can be eaten raw, but only if it is cleaned before eating. As you said, there are risks of parasites and eggs on the surface of lettuce, so before eating lettuce, it is best to clean it, clean up the drug residue and egg adhesion on the surface of lettuce, and blanch it a little to ensure the safety of eating lettuce to the greatest extent.
The picture comes from the internet.
So, to sum up. Lettuce can be eaten raw, but it also has the risk of parasites, so it should be cleaned before eating raw. As long as it is cleaned, it can be eaten raw, just like cold cucumber.