Half the applications only 1 per week and my mouth sores and swelling [SEP] I’ve used this twice ...  they thought of everything from lip gel to the neck cord so you can move around ...  BUT each time after the first of the 5 applications and only 3 not 4 back to back my lips swelled up and had painful sores inside my mouth ...  I reapplied the mouth gel carefully with each use of the mouthpiece too !  I have never had an issue with other whiteners ...  gong back to crest strips :/