There was something in the news about dry shampoo being bad for you.
They said that it can cause hair loss but lots of things cause hair loss and there is no scientific proof this product is to blame, to my knowledge so far. I read something about Pantene causing issues if you went to the hairdressers and had bleach applied but again not read any proof.
Anyway back to the topic, I wash my hair before my first booking and inbetween the second, just spray something nice and smelly to disguise the smoke smell that clings to hair. I don't tend to dry may hair after a shower so some clients have guessed that this means they are the first booking. If that's the case then just wet and spray it so they think they are the first.