All whitening gel causes some degree of tooth sensitivity. This is discomfort due to hot and cold fluids, and sometimes even air. This is normal and an expected side effect. If your teeth do become sensitive, try completing the treatment every second day or reduce duration. Sensitivity should disappear completely within 1-3 days after completing the treatment. The You still achieve the desired results, it will just take a little longer. Gum irritation can also occur, especially if you overfill your retainer.You will notice that your gum will become white, however, this will disappear shortly after you stop your treatment. You can also place vitamin E oil on the affected area to reduce irritation.