WordPress automatically removes any HTML that appears in user profile bios (bios). This is a little piece of code that permits HTML in author bios.
Very easy to do: simply add the following code to the functions.php file of your plugin or theme:
remove_filter('pre_user_description', 'wp_filter_kses');
This disables the wp_filter_kses filter from the user description by using remove_filter(). This code, if included, will allow you or any other user to annotate a profile description with markup.