What are some potential pitfalls or issues that can arise when dealing with recursion in PHP?

One potential issue when dealing with recursion in PHP is the risk of running into a "maximum function nesting level reached" error if the recursion depth is too high. This can happen when a function calls itself too many times, causing PHP to reach its maximum recursion limit. To solve this issue, you can increase the maximum function nesting level in the php.ini file or rewrite the recursive function to be more efficient and avoid excessive recursion.

// Increase the maximum function nesting level in php.ini
// Add the following line to php.ini
// xdebug.max_nesting_level = 1000
```

```php
// Rewrite the recursive function to be more efficient
function factorial($n) {
    if ($n <= 1) {
        return 1;
    } else {
        return $n * factorial($n - 1);
    }
}