Fresh, minty and lightly sweet! SunnaSmile whitening gel will not make much contact with your tongue (it's ok if it does) so you likely won't notice a taste to the gel at all.
The SunnaSmile product has been tested for safety and will not be harmful if swallowed however we strongly encourage our clients to limit as swallowing as possible. Try to sit up straight during the service and wear a dental bib as well as have a towel handy for drool to help eliminate swallowing.