So no washing your hair at all?

Or is there some whitelist of allowed chemicals? I assume at least water, but hopefully some kind of surfactant, too?

And no, I’m not being obtuse, I genuinely never know what people mean when they say things like this. Same as eating “clean”. It usually seems to be “clean means food that seems intuitively healthy to me” and “chemicals are things that seem intuitively scary to me”.