What security considerations should be taken into account when processing user inputs in PHP?

When processing user inputs in PHP, it is important to sanitize and validate the data to prevent security vulnerabilities such as SQL injection, cross-site scripting (XSS), and CSRF attacks. Sanitizing involves removing any potentially harmful characters or code from the input, while validating ensures that the input meets the expected format or criteria.

// Example of sanitizing user input in PHP
$userInput = $_POST['user_input'];
$cleanInput = filter_var($userInput, FILTER_SANITIZE_STRING);
```

```php
// Example of validating user input in PHP
$userEmail = $_POST['user_email'];
if (filter_var($userEmail, FILTER_VALIDATE_EMAIL)) {
    // Input is a valid email address
} else {
    // Input is not a valid email address
}