In order to bleach your teeth to give you that white smile you desire, products like a teeth whitening pen contain harsh chemicals designed to weaken the enamel. As the chemicals within the product weaken the enamel, it makes your gums and teeth be very sensitive. While there are Sensitive Teeth Tooth whitening products available, even these can cause problems with the harsh chemicals.
As the chemicals work to make your teeth prone to bleaching, the teeth whitening products leave your mouth open for hives and other painful side affects. If you have any degree of allergy to similar products, you will react even more to these as they make the surfaces of your gums and teeth raw in the process of giving you the whiter teeth you want.
If you want to avoid having teeth whitening products causing hives and other side affects, you should check with your dentist or family doctor and find out what substances may cause this problem for you so you can avoid them. Laser teeth whitening technology may be the solution for you, as exposure to any harsh chemicals is restrained to one visit to the dentists.
Once again, this is something that you should ask your dentist and doctor about, as an allergic reaction in the mouth can cause a great many problems for you in the short term and in the future. With a little care, you should be able to find a product that will not cause you any problems and get the white smile you deserve.