Capsaicin, the active ingredient in cayenne pepper, kills many types of bacteria -- friendly and non-friendly. It also kills many parasites, including candida.
There is no such thing as a substance which can selectively kill the bad parasites while leaving the friendly bacteria intact. This is a myth, and is not supported by any studies that I've been able to locate.
This is also true with garlic: it kills the good along with the bad.