Are there any potential pitfalls in manually replacing special characters in email subjects in PHP?

When manually replacing special characters in email subjects in PHP, potential pitfalls include accidentally removing essential characters for the email to be properly displayed or breaking the encoding of the subject line. To avoid these issues, it's important to use proper encoding functions to ensure the subject line remains intact and readable.

$subject = "Hello, this is a subject with special characters áéíóú";
$subject = mb_encode_mimeheader($subject, 'UTF-8', 'Q');