What are the characteristics of miniaturized hairs?

[Autumn Sundown]

I have some hairs on my hairline that never grow. They're black (like the rest of my hair) and very thick, about the same thickness as the hairs from the back of my head. I don't notice them shedding and they're very hard to pull out. All the hair behind them is very, very thick.
I first noticed them about 5 years ago. No more have appeared and my hairline is in the same place.
I was just wondering if this is something I should be concerned about.