A function like htmlentities

Hi
First excuse me for my English and for my technical knowledges in PHP (I'm a novice)!

I wanted to know if ckeditor provides a function "like htmlentities".
I explain you my problem: I have a ckeditor textarea zone. In the next page, im doing an update of my database with the text of my textarea. But anyone can change the html source code and modify the text beetween <textarea></textarea> to put a <script> for example. So, I need to check in the next page my datas but if I apply htmlentities, I will loose the layout of my ckeditor text.

So is there a function that can keep the <p></p> (etc...) coming from ckeditor but which would erase <script> and the other "bad" html code.

I hope you understood me!
Thank you!!!