Opposition groups in Syria are claiming anew that the Syrian government used chemical weapons against them. This time, they say, the attack killed over a thousand people, including children. The Assad regime has denied the claims, and United Nations inspectors in the country have not been able to independently confirm or deny them.

It’s not known what type of chemical weapon might have been used in the attack. But how do different kinds work and what makes them so terrifying?

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A handful of chemicals rank among the most feared as potential weapons, according to HowStuffWorks.

On the less-threatening end is sarin, a clear and tasteless manmade liquid, which the Syrian government is rumored to have, according to the BBC.

Sarin affects communication between nerve cells by interfering with an enzyme called cholinesterase, which works to flush out a message-carrying molecule called acetylcholine. By knocking out the off-switch normally provided by cholinesterase, HowStuffWorks explains, sarin causes uncontrollable contractions of the muscles, including the diaphragm. Suffocation can follow.

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Sarin evaporates quickly. So, although it can be deadly, it poses only short-term threat. But Assad’s regime is also thought to have mustard gas, a blistering agent that damages the skin, eyes, respiratory tract and even DNA. Extreme exposures can cause blindness and death.

Worst of all, the Syrian government may also possess VX, a liquid nerve agent that is 10 times more toxic than sarin. VX works like sarin does, but it is much slower to evaporate, meaning that it can last for days to months, presenting a serious and ongoing threat to people who come in contact with it.

Chemical weapons have the potential to cause massive and unprecedented amounts of damage.

“This is unknown territory,” Charles Blair, senior fellow for State and Non-State Threats at the Federation of American Scientists told The Christian Science Monitor. “We have never been through the potential collapse via a very bloody ethnic civil war of a country that is likely armed with a very large stockpile of chemical weapons.”

Image: Syrian protesters Credit: Getty