Since Darkhorse brought this up, so I thought I would borrow her comment for this:
My scalp always knows when the seasons change. I always wonder if it has something to do with sweating. We sweat more in the summer, and I wonder if that does something to the scalp that, when the cooler weather comes, is it irritable? Less moisture? Is something growing in there? For me, I have to wash, but I was using a special conditioner for my scalp once our temps dropped to what I call reasonable, and since our temps went back to August like (boo!), my scalp isn't cranky, but I am because I like the cooler autumn weather :DMy working theory on this is that season changes, especially for autumn messes with both the scalp and length of hair.
Just something to make you go 'hmmmmm...." :D
For the scalp:
The acid mantle which forms the protecting layer on your skin (And scalp) is formed by three things: Your sweat which contains lactic acid to maintain the right pH value, the sebum which helps to waterproof the skin (Both for penetration and evaporation) and the dead skin cells (Epidermis) which physically shields the skin.
So autumn is cold and rainy outside, and warm and dry inside and you start wearing hats more.
I could see you sweating more and not even noticing...
Also I could see you producing more sebum to keep the moisture inside your skin?
For the length:
As for the weird "irritated" reaction I get on the length, my best guess is: Hair contains 8-10 % water and it can absorb and release water depending on the surrounding environment. The little "scales" that covers the hair can't to do this, but the inner core of the hair (The cortex that contains the protein bundles which give hair its strength) can.
I imagine it would be like repeatedly steaming and drying wood. It should feel really strange, and I guess eventually it should crack and split.
Anyways. I'm just guessing and putting what little I know together.
...Anyone have some knowledge on this?