Geostigma is effecting the children and Cloud. People are thinking that Aerith is at least partially responsible for it, since the Lifestream washing over people at the end of FFVII is probably how they got it. Here's how Vincent explains what Geostigma is.

From the report on the Montreal Film Festival at Daeya.org:
[Vincent] goes on toe explain that there is a current resembling the Lifestream in their bodies that fight off invading alien matter.... Vincent continues by clarifying that when the body overcompensates for the unwelcome guest, the result is Geostigma... he continues by saying that the alien matter in this situation is the Sephiroth gene. He also gives another name for it, "Jenova's genetic legacy". Confirming Cloud's suspicions, he says that the Mother that Kadaj is so actively looking for is "Heaven's dark harbinger, Jenova." He then goes on to reveal the startling truth that if need be, another Sephiroth can be created.

From the Venice Film Festival:
Vincent: "Geostigma is the reaction of human bodies that are trying to expel some toxins... Sephiroth' s gene, Jenova' s cells, however you may want to call them. There is a thing like the Lifestream that flows in our bodies, and it is fighting against the wicked substance that has penetrated us. Geostigma is the result of all that."

From this, we can tell that those who suffer from Geostigma have Jenova cells in them. The Lifestream within people is fighting against the Jenova cells. The Lifestream (where Aerith is) is fighting the Jenova cells. This brings up some interesting questions:

1. How did the children get Jenova cells in them? Were Jenova cells in the Lifestream when it covered the Planet in the final FMV to destroy Meteor so that everyone was exposed? If so, how did Jenova cells get in the Lifestream? The theory now is that Jenova cells got in the Lifestream from Jenova's head being adrift in the Lifestream as Sephiroth drifted from Nibelheim to the Northern Crater.

2. Why does it seem that mostly children have it? Why is Marlene the only child we've seen who doesn't have it? Is Aerith keeping Marlene healthy?

3. Cloud already had Jenova cells in him before getting Geostigma. Will that make it harder for him to heal?

4. If the Lifestream is fighting the Jenova cells, is it possible that Geostigma can affect Aerith's spirit? Or does it suggest that Aerith will somehow help fight against it?

What are your thoughts?

1. How did the children get Jenova cells in them? Were Jenova cells in the Lifestream when it covered the Planet in the final FMV to destroy Meteor so that everyone was exposed? If so, how did Jenova cells get in the Lifestream? The theory now is that Jenova cells got in the Lifestream from Jenova's head being adrift in the Lifestream as Sephiroth drifted from Nibelheim to the Northern Crater
I think it is possible these children became orphans cos their parents died during the final battle period,perhaps when meteor came down or when the lifestream explodes and things like that. Somehow, these children were more resistant than their parents, thus they survived. Geostigma is like a virus, once you have a wound, the jenova cell gets into you, it causes a reaction in your body. So these children could have possibly gotten themselves hurt during the final battle period, and the jenova cells got into them when the lifestream explodes (I have read a theory about Jenova cells being in the lifestream :huh: - cos remember when spehy was first killed by cloud at nibelhelm, he was thrown into some depth of a hole? and possibly gets mixed with the lifestream. It was a very beautiful theory of about cloud and his struggle against sephy and jenova but i cann't remember where i read it now! lol)

2. Why does it seem that mostly children have it? Why is Marlene the only child we've seen who doesn't have it? Is Aerith keeping Marlene healthy?
I think it's very possible! She was the only one that pointed out "the flower girl" during the final battle afterall.

3. Cloud already had Jenova cells in him before getting Geostigma. Will that make it harder for him to heal?
Yes, it will be very difficult in my opinion because CLoud has huge doses of jenova cells in him(injected during the experiment). It will be a huge internal battle for Cloud.

Have anyone ever think about this? What if lifestream or Jenva won the "battle"? What would happen?
I think if jenova wins, he'll officially become Kadaj's big bro. lmao

1. How did the children get Jenova cells in them?

I think it's because their fathers are from SOLDIER. I remember Wheel-chaired guy saying that Cloud is the only ex-SOLDIER left, and I don't know if there are any SOLDIERs left in the setting of AC. Anyway, it's possible that their mommies and daddies died because of Geostigma, because I *think* that SOLDIERs are enhanced with JENOVA/Mako technology? (I vaguely remember something like that...?)

I think it's possible that the children may have inherited the Jenova cells from their parents. Since, you know... cells divide, multiply. Meiosis. Heheh.

2. Why does it seem that mostly children have it? Why is Marlene the only child we've seen who doesn't have it? Is Aerith keeping Marlene healthy?

Going with my cockamamie theory written up there, Marlene's dad didn't have JENOVA in him. And I think other children who aren't infected aren't significant to the story. (THough the Aerith theory is interesting.)

3. Cloud already had Jenova cells in him before getting Geostigma. Will that make it harder for him to heal?

Maybe... I think he has a more simple case of Geostigma, though...

4. If the Lifestream is fighting the Jenova cells, is it possible that Geostigma can affect Aerith's spirit? Or does it suggest that Aerith will somehow help fight against it?

I hope it suggests the latter. ;)

Zhak and I have discussed this before... ^_^

...but just to add to her answer in number two regarding the question "why only the children has Geostigma":

Because they are the generation born after their fathers had been exposed to Mako energy. In the case of Cloud Strife, he was SOLDIER and had been exposed to Mako as part of the program... as for Rufus, well, it's possible he could've been experimented upon as a child...

Well at least that's what I can think of... as of now... <_<

Marlene doesn't have Geostigma because maybe her father hasn't been exposed to Mako energy...

Hmm...

Come to think of it? Could Aerith be the cure for Geostigma? <_< Okay,,,, my mind's doing it again... must stop it from flying too much... :unsure:

Heeey! Zhankeeka! Good point! That could quite possibly be very true!!
Or maybe we all just have a lil Jenova in us, huh?*...smiles...*