I am simply amazed at this simple to use product. A tip for anyone that may experience cold intolerance, use the pen less often and tough it out. Mine went away in a few days. However, the difference it made in the whiteness of my teeth is simply amazing. My only complaint is that any product I got on my lips caused my lips to chap. I solved this by putting on a Vitamin E lip balm prior to using the pen. I am more than satisfied and will purchase again.