I think it must be dry skin. When I was a child, I will scratch my arms in the outside when it is sunny. I could see lots of particles (dry skin) flying. It is not a big deal. And I had never worry about that before. Maybe you thought that I was dirty and need to take a shower. But actually I was clean enough. My skin is very dry. I need to moisten them.
It could be fibres, dust in the sky. But it could be eye floaters which happen to many people. If you see lots of eye floaters in your vision, you'd better visit your optometrist immediately because it could be a starting sign of some eye disease. Hope this helped!