If by whitening you mean a dentist-administered bleaching treatment, it is currently thought to present little risk except for some short-term soreness of the gums and a transient increase in tooth sensitivity to heat, cold, contact, and sweets. It is a relatively new technology, and the long term cumulative effects, if any, are not known. This may be significant, since bleaching may need to be repeated at indefinite intervals to maintain the whitening.

The same degree of safety cannot be assumed for unregulated over the counter bleaching agents, due to the unknown nature of their content.