The last time I washed my hair was Sunday and I do not plan on washing it before this Sunday. My goal (for the past ~2 years) has been to stretch washes to once a week.
But why would anyone want to do that? I think of it like this: if I bought a cotton t-shirt and washed it every day by the end of the first year it would be ruined. I figured that if I plan on growing to classic length, it will take me about 6 years and if I wash my hair every day that equals 2,190 washes total! My ends would be a mess and so would most of my length.
"I have previously blogged about hygral fatigue which starts off when hair strands expand when wet and then contract when dry. Repeating this process several times can create damage to the hair cuticle first because it can be chipped off and then later damage to the main strand leading to split ends/breakage etc. It is not really about too much water but really just water, full stop. " (source)
I do minimize such damage by using a gentle non-sulfate shampoo and stretching washes (I’ve experimented with other milder options than the regular SLS shampoo that’s so popular right now). I also only wash the length with shampoo once in a while and when I do I protect it by doing a pre-wash coconut oiling which has been proven to minimize protein and moisture loss and mechanical damage during washing. I also don’t pile my hair on top of my head or rub it with a towel after, which pretty much eliminates tangles born during washing and lowers the mechanical damage that can be caused by combing tangles out.
Something as simple and easily ignored as washing hair often can have a huge effect on hair. While chemical dyes and heat styling is known by most to be damaging, mechanical damage can be overlooked. I pay attention to all the damage my hair can go through and try my best to avoid it.
But what does this have to do with my scalp? The scalp produces it's own oils (more like wax) called sebum. Harsh shampoos and washing hair often can strip the sebum and cause your scalp to either be very dry or rebel and produce even more sebum to make up for the one that was stripped off. This can lead to hair problems like perpetual greasy scalp, itchy scalp and extra shedding, etc.
There are people who either don't use any shampoo, or just use water to wash their hair, there are even some out there who don't wash their hair at all. I mention them because they usually go through a normalization period that can last a few weeks or a few months, after which their scalp stops producing extra sebum and their hair looks clean and nice. This shows that for some at least treating your scalp gentler can help with issues it usually has.
There are those few that can't get good results with stretching washes because of some scalp condition such as seborrheic dermatitis or psoriasis, etc. And others benefit and calm down their issue with gentler scalp cleansing. Everything to do with hair treatment is pretty much dependent on genetics, diet, environment etc, so one thing might not always work for everyone. I think stretching washes is at least worth a try. That's just me though.