Is it okay to use mouth wash with retainers on?

Yes: Yes, but better to take the retainers off since they may prevent the mouthwash from accessing all surfaces of your teeth.

Generally Not: Mouthwash can damage the surface of your retainers over time...It's too aggressive for most plastic materials. In addition, the mouthwash won't reach all the areas of your mouth/teeth when the retainers are in the way, so it won't give you the maximum benefit. There's really no advantage to keeping them in while you're rinsing.

Yes: However removal of your retainers will allow the mouthwash to access all of the areas covered by your retainer. Most mouthwash contains alcohol, this should not cause damage.