In this new post to Reddit, the author shares a bit of their knowledge on what they think everyone should know about strip_tags and some of the issues that can come with it (including security problems).

strip_tags is one of the common go-to functions used for making user input on web pages safe for display. But contrary to what it sounds like it's for, strip_tags is never, ever, ever the right function to use for this and it has a lot of problems.

Specific problems mentioned include "eating" of valid text, not preventing typed HTML entities, the whitelist of tags opening holes and character set issues that could have security implications. Other tools are recommended in both the article and the comments like HTML Purifier, the option of BBCode and Markdown.