What considerations should be made when handling user input data in PHP to prevent special characters from affecting the CSV output?

When handling user input data in PHP to prevent special characters from affecting the CSV output, it is important to sanitize the input by using functions like `htmlspecialchars` or `mysqli_real_escape_string` to escape special characters. Additionally, it is recommended to use proper encoding techniques to ensure the data is properly formatted for CSV output.

// Sample code snippet to sanitize user input data before writing to a CSV file
$userInput = $_POST['user_input'];

// Sanitize user input to prevent special characters from affecting CSV output
$cleanedInput = htmlspecialchars($userInput, ENT_QUOTES);

// Write the sanitized input to a CSV file
$csvFile = fopen('output.csv', 'w');
fputcsv($csvFile, array($cleanedInput));
fclose($csvFile);