What makes periods more "gross" than blood from other areas?

What do you think makes period blood more gross than blood from any other area to some

If you're distressed about by any blood feel free to say so, but the phobia isn't the answer I'm looking for. I'm talking more specifically to people who are okay with any other blood, but somehow are grossed out by periods. If you're not disgusted by one over the other, can you try to explain why?

I personally think it's ok to be grossed out a little, just as with any other bodily fluid, but I truly do not understand why some people are more disgusted by menstral blood. Yes, it has a different smell than say a scraped knee, but so does a nosebleed. I'm almost offended by it, women can help this no more than having to shit once in a while. I feel like this is prbably linked to creating taboos about either sexes body, and gender roles.

What do you think about people like this? The idea itself? Where did it come from? How does it make you feel as a woman (or man)?