Possible soap/dandruff buildup?
is it lint?? I had like a single piece or two of lint once. I had asked a friend about this and was told it happens sometime and isn't always easy to get out, but my impression was that it was harmless.
Or, if it's definitely not lint, I mean, it also kinda looks like...well, two thoughts. I'm thinking sometimes I'll get that when I use tightening sprays...or it could maybe be hair tips poking out, like the hair follicle bits that fall off as your hair grows out.
Does it smell or is it greasy when you squeeze it through your fingers? I had residue from using soap (yeah, ignorance) in it and when I'd squeeze it through my fingers over it, I'd pick up the smell/residue of the soap. That's how I knew. Sadly, I had to comb mine out, but others here might be able to help better. Actually, I've since heard of clarifying shampoos. I believe Neutragena has this.
Well, hopefully someone else posts because I'm no expert, but this has been my experience with daily interest and observation for almost 2 years.