But then how come the streak on my dress was a really dark looking red

Okay so period blood can look really dark sometimes, even almost black, especially when it's just a little bit or if it's been sitting on your clothes for a bit. It’s totally normal and usually means it's older blood.

See, when blood leaves your body, it reacts with the air, and that can make it change color. So if it was on your dress for a while before you noticed, or if it was just a slow drip, it had more time to get exposed to the air and turn darker. Usually, fresh blood when you're actively bleeding is more of a bright red, but it can be all kinds of shades throughout your period.

Period blood color can change a lot during your cycle. It can be bright red, dark red, brown, or even black. It's usually nothing to worry about. But if you ever feel really worried or have super heavy bleeding that soaks through pads or tampons every hour for a few hours, then it's a good idea to talk to a grown-up.