Why does bleaching teeth hurt so much?

Sensitive nerves: Teeth are made up of tubules containing nerve fibers. The bleach is taken up in the tubules and causes irritation of the nerve tissue. Using a desensitizing toothpaste for 2 wks. Before and while bleaching helps reduce the sensitivity. Also taking ibuprophen helps.

A few things: If probably is due to sensitive roots of your teeth. Often if there is root exposure or gum recession around the teeth, then it can be painful. Consider having flouride treatment to reduce the sensitivity. Also, you can use a lower strength peroxide or decrease the frequency of the times bleaching is done.