Okay, then what you're seeing underneath the oil cap is probably just condensation from short duration drives. The condensation which typically accumulates inside an engine is normally burned off by driving the car on longer duration drives, but since your commute to work is relatively short, the engine oil never gets up to 212F, which is the temperature it needs to reach in order to boil off the accumulated condensation.
It isn't great for your engine, but it isn't the end of the world. One additional bit of advice: Don't let your car warm up in the morning by idling it. Just start it up and drive away normally. Many people people think they're doing their engine a favor by warming it up by idling before driving away, but this causes the warm-up process to take much longer compared to if you get in and drive. This may or may not apply to you, however, but I thought I'd just throw it out there for everyone.
1998 BMW 328is
1966 Pontiac GTO
2007 Subaru Impreza 2.5i 5-door
View my photos: Caught in the Wild