"Hygienic idempotency and creative reverie: Yet another male privilege?" is going to be my Gender Studies dissertation.
If you use shampoo, it's not idempotent. Over-shampooing hair dries out your scalp. A nontrivial number of guys with dandruff could benefit from shampooing less often.
I've been wondering about this. I have a bit of dandruff.
I really like the fluffy hair feeling i get when i wash most/all the grease out.
But sometimes i can wash my hair 4-5 times and it's still greasy!