Dry shampoo, unlike its wet counterpart with water (sorry for the tautology), is able to remove only fat, which is sorbed on lipophilic particles and shaken off. The main function - to wash the hair - this tool does not perform. And yes, the hair looks clean and dry, but in fact, all the dust, chemicals trapped by the hair in the city (acid rain, for example) remain on the hair. Dry shampoo itself is not harmful, but it is much more beneficial to rinse your hair, even with just water.
It seems to me more harmful. Dry shampoo contains absorbents that "absorb" oil from the hair and scalp. Because of this, he can dry out his hair. Even if you only pour on the roots, you still need to comb it along the entire length.
I periodically use dry (Lashevsky), the roots are normal, but the length then looks like a washcloth, I struggle with the desire to push the ends to the middle under the tap to make them less nasty.