Some people experience temporary tooth sensitivity during treatment. Others have reported discomfort in the gums or in loose fillings. Gum irritation usually disappears within 1-3 days after beginning the procedure and always upon the discontinuation or completion of treatment. There are no other significant side effects. YOU SHOULD NOT USE THIS PRODUCT IF YOU ARE PREGNANT, HAVE HEALTH PROBLEMS, PERIODONTAL DISEASE OR GUMS THAT ARE IN POOR CONDITION, WEAR BRACES, HAD RECENT ORAL SURGERY, DECAYED TEETH, HAVE ROOTS THAT ARE EXPOSED, HAVE COLITIS, OR HAVE JAW PROBLEMS. The manufacturer and seller assume no responsibility for any usage of product. You should consult with a dentist before attempting any at-home treatments and understand that there are risks involved if not doing so. A small percentage of people may experience temporary tooth sensitivity and gum irritation which disappears when use ends, or by decreasing the amount of time you bleach your teeth each time, or by increasing the amount of time between bleaching sessions.