What is the potential risk of using htmlentities on post variables in PHP?

Using htmlentities on post variables in PHP can potentially introduce a security risk known as double encoding. This occurs when the data is already encoded before being passed to htmlentities, resulting in the data being encoded twice and displayed incorrectly. To solve this issue, it is recommended to use the PHP function htmlspecialchars instead, which will properly encode special characters without double encoding.

// Using htmlspecialchars instead of htmlentities on post variables
$encoded_data = htmlspecialchars($_POST['input_data']);