The ingredients for the lethal substances apparently involved in the poisoning of Sergei Skripal are easy to obtain and are usually absorbed quickly through the skin or inhalation

After days of analysis, police investigators announced on Wednesday that they believe a nerve agent was used to poison former Russian agent Sergei Skripal and his daughter on Sunday, raising questions of how it was created and how the attack was carried out.

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A range of highly potent nerve agents were developed by military scientists from the 1930s onwards and a number have since been used in assassinations and terror attacks. On Tuesday, the US state department confirmed that it held Kim Jong-un’s North Korean regime responsible for the murder of his estranged half-brother, Kim Jong-nam, in Kuala Lumpur international airport last year. The Malaysian authorities have charged two women with Kim’s murder after they allegedly sprayed the nerve agent VX on his face. The two maintain they were duped into the attack, claiming they thought were being filmed for a TV prank show.

In the 1990s, the Aum Shinrikyo doomsday cult in Japan used VX to kill dissenters before releasing another nerve agent, Sarin, in the Tokyo subway, leaving more than 600 people in need of treatment. More recently, Sarin was used by the Syrian government in the civil war that has ravaged the country since 2011.

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Nerve agents are not hard to make in principle, but in practice it takes specialised facilities and training to mix the substances safely. The raw materials themselves are inexpensive and generally not hard to obtain, but the lethality of the agents means they tend to be manufactured in dedicated labs. The main five nerve agents are Tabun, which is also known as GA and is the easiest to make, Sarin, Soman, GF and VX.

VX was invented in the UK in the 1950s, and is the most powerful nerve agent. It is mostly absorbed through the skin, and tends to take effect in the space of minutes. It can also be turned into a vapour by heating it, in which case the effects are almost immediate.

Because it is particularly stable, it tends to remain on clothing, furniture and the ground for a long time, meaning it can be detected on samples collected from areas where it is used. But because of its potency and persistence, people attacked with VX are themselves a danger to first responders who can fall ill when they come into contact with minute traces of the agent. The victims must be decontaminated and affected areas cordoned off until they can be made safe.

In pure form, all nerve agents are colourless organophosphorus liquids. They were found to be highly poisonous in the 1930s and became the dominant chemical weapons of the second world war. Once made, the substances are easy to disperse, either as liquids or aerosols, are highly toxic, and have rapid effects. Most are inhaled or, as is the case with VX, absorbed mostly through the skin, but in liquid form they can also be added to food and drink, which delays the onset of their effects.

The agents take their toll on the body by disrupting electrical signals throughout the nervous system. The effects are fast and dramatic. People exposed to nerve agents find it increasingly hard to breathe. Their lungs produce more mucus which can make them cough and foam at the mouth. They sweat, their pupils constrict, and their eyes run. The effects on the digestive system trigger vomiting. Meanwhile the muscles convulse. Many of those affected will urinate themselves and lose control of their bowels. At high doses, failure of the nerves and muscles of the respiratory system can kill victims before other symptoms have time to develop.

There are antidotes for nerve agents, such as oxime and atropine, both of which are used in military devices that deliver quick shots to victims. The antidotes are particularly effective against VX and sarin, but they must be given soon after exposure to work.

Chris Morris, a medical toxicologist at Newcastle University, said: “If the symptoms can be controlled until the agent is removed then recovery is good. With the type of supportive care given in these cases, there may be minimal long term effects if treatment was rapid and effective.”