It's a waste product, and is made up of a little blood and mostly body tissue
You are basically carrying around rotting matter. This starts to smell the moment it has contact with the air, getting worse the longer you leave it. This is why personal hygiene is so important when you are on the blob.

It's also why mooncups fit internally, so the menses doesn't have contact with air until you remove it for cleaning.
( Wicca'd Witch needs ideas for a new sig on..., Sun 2 Dec 2007, 21:51, archived)

It's not in contact with the air;
it's rolled up tight in a wrapper.
( Bob Todd whee, Sun 2 Dec 2007, 21:52, archived)

Bollocks, the wrapper is not sealed and they've been in there for two days.
THEY WILL SMELL AND SO YOU WILL YOU, YOU JUST DON'T NOTICE YOUR OWN STENCH.
( Wicca'd Witch needs ideas for a new sig on..., Sun 2 Dec 2007, 21:58, archived)

You seem to be under the impression I'm carrying around a nappy full of bacon rashers.

( Bob Todd whee, Sun 2 Dec 2007, 22:00, archived)