What is a seroma? A seroma is basically a fluid pocket with serous fluid in a dead space that contains plasma and lymphatic fluid. When telling my clients to be aware of these, I often refer them to a "waterbed" look. This will be a slight to large bulge in the skin that is usually soft and resemble the movement of a waterbed. Most of the time the seroma will go away on its own, but if it does not I do recommend clients to go to there PC physcian to drain it.