What do you call this phenomenon?

I call it the shampoo effect. Do you ever go a few days without washing your hair (because you are camping, lazy or otherwise), and then when you shampoo your hair that first time back, it doesn’t really take – you wind up having to shampoo it again? The first time it doesn’t froth up the bubbly way you’ re used to, but that second round of shampooing does the job. Anyone out there experience this, or am I crazy?