Counterterrorism police in the UK have today confirmed that a former Russian spy who worked for the British Intelligence Agency MI6, Sergei Skripal, and his daughter Yulia, fell into a critically ill condition this week after deliberate "exposure to a nerve agent".
The police officer who first attended the scene is also seriously ill in hospital. All of them are suffering from exposure to the nerve agent, which the police have now identified.
Nerve agents have been described as the most dangerous thing humans have ever made, other than the atom bomb. So what are they, exactly?
What are nerve agents and what do they do to your body?
Nerve agents are highly poisonous chemicals that prevent the nervous system from functioning properly. There are several different types, including Sarin, Tabun, VX, and Soman.
They all work in a similar way, overstimulating your nervous system, causing your muscles to contract uncontrollably.
VX, short for venomous agent X, makes you unable to breathe within a matter of seconds or minutes, depending on the dose and whether it was ingested or administered through skin contact.
Early symptoms of VX poisoning include vomiting, shortness of breath and a runny nose. However, the toxin acts so quickly that there is rarely time for treatment before death.
Sarin, mainly administered as a gas, also causes respiratory failure, convulsions, loss of consciousness, diarrhea, paralysis, excessive drooling, and sweating, according to the Centers for Biological Diversity (CDC).
White eyes (due to constriction of the pupils) is also common in victims of poisoning.
How do they work?
Nerve agents all target the cholinergic system. The agents target an enzyme in the space between nerve cells and muscle cells (known as synapses), Business Insider explains.
When you're functioning normally, nerve endings release acetylcholine. When this touches a muscle it causes it to contract. The enzyme acetylcholinesterase then sticks to the acetylcholine, disabling it and causing the muscle to relax again.
However, nerve agents disrupt this process by attaching to the enzyme. This causes a buildup of acetylcholine in the muscles, making them go haywire, resulting in all the horrible symptoms listed above.
How are they administered?
Very, very carefully.
Nerve agents are extremely toxic. Wearing protective clothing is no guarantee that the person administering the dose will be safe. The toxins come in several forms, including gas, powder, and liquid. They need to be inhaled, ingested or make it through the skin of the target in order to take effect.
Have they been used before?
Yes, sadly. Many times. In 1995 in Tokyo, sarin was released into the city's subway system as part of a coordinated terrorist attack. Thirteen people died and 5,500 were injured.
Last year Kim Jong-nam, North Korean leader Kim Jong-un's half-brother, was assassinated using banned nerve agent VX. His assassins walked up to him at an airport and put the liquid on his face using a cloth. He died shortly afterwards.
Also last year, a sarin attack took place in Syria that killed more than 80 people, and drew condemnation from leaders all around the world.
How are they made?
These are not easy chemicals to make. You won't be making these in a makeshift lab in your bedsit flat. Which is one reason why the British government thinks involvement at a state level is a possibility. These drugs need to be made in industrial laboratories. Fortunately, this also makes them traceable, which may work in the British police's favor.
Only the US and Russia have ever admitted to possessing nerve agents, although other countries are suspected of having stockpiles in their possession.