The thing with not washing hair, is that oil production is different for every person, especially age groups.Typically, the older you get the less sebum your scalp produces, so the longer you go between shampoos, the more naturally moisturized your hair is. On the other side, the younger you are, the more sebum your scalp is producing so the "dirtier" your hair feels. When that happens, we usually grab dry shampoo. Dry shampoo can congest your scalp when applied over and over. When the scalp has too much build up, it cannot work to the best of it's ability. Over time, this can lead to hair loss, delayed hair growth, and overall dullness and dryness.
To expand as simply as possible, the scalp is still skin and has pores; you can't have healthy hair without a healthy scalp. There are tons of products on the market aimed at creating healthy scalps to optimize hair growth. Using dry shampoo over and over for extended periods of time will indeed clog your pores and can lead to painful scalp conditions like infected hair follicles. A congested scalp will also bring on loss of hair. It is important to also maintain the pH balance of your scalp. If your scalp doesn't maintain a proper pH level, it can lead to bacteria growth, dryer hair strands, itching, flakiness, etc,.
I'm not saying that dry shampoo is all of a sudden bad, it's not; it's definitely one of my favorite products ever. Rather, I think it's very important for people to know that dry shampoo is not a substitute for a good cleansing of your scalp. When used properly, dry shampoo is a great tool to extend the life of shampoos or a touch up after the gym. However, it's not "cleaning" your scalp or hair and using it day in and day out over long periods of time will lead to less hair and dryer hair!
I've tried dry shampoo FOAM and it's out of this world. I like dry shampoo because it's dry which, in my mind soaks up more oils; so the idea of putting a foam (wet) into my greasy hair didn't sound great. Like any product junkie, I still tried it out. First, on my one day dirty hair and I didn't notice a huge difference, aside from added volume at the root. I decided to try again on dirtier hair topped with a trip to the gym. Money. This stuff worked so well! The difference between the foam and typical dry shampoos is the cleansing capabilities. My hair actually felt as clean as it looked. The magic is in the formulation. It's made similarly to the stuff they use in hospitals when you can't wash your hair, but with higher-end ingredients for a friendlier experience. Also, it smells amazing.