What are the potential security risks associated with not properly handling special characters and HTML tags in PHP applications, especially when dealing with user input?

Improper handling of special characters and HTML tags in PHP applications can lead to security vulnerabilities such as cross-site scripting (XSS) attacks. To mitigate these risks, it is crucial to properly sanitize and validate user input to prevent malicious code injection.

// Sanitize user input to prevent XSS attacks
$user_input = htmlspecialchars($_POST['user_input'], ENT_QUOTES, 'UTF-8');