Cut or break the bottom of a leaf of romaine lettuce and you may see a strange milky liquid seep out from the stem where it broke off. While it may look a bit ominous, there's no need for alarm.
What Is the White Sap?
The white sap is a milky fluid made of latex that's naturally found in the lettuce and is completely harmless.
The botanical name for the substance is lactucarium, which comes from lactus, the Latin word for milk (the botanical name for lettuce is lactuca sativa, which also stems from this word). The white sap is a little bitter and, interestingly, has a sleep-inducing compound. Ancient varieties actually contained a much greater amount of this sap, so much so that Romans served lettuce at the end of a meal to relax and encourage sleep.
Over time, the amount of sap in lettuce has diminished, so there's no need to worry about that Caesar salad putting you to sleep. If you do notice a little white liquid coming out of the base of your cut or broken romaine lettuce, while it may taste a bit bitter, it's completely safe to consume.