It looks and tastes like alcohol, and the first effects are similar – it can make you feel intoxicated and sick.
Initially, people might not realise anything is wrong.
The harm happens hours later as the body attempts to clear it from the body by breaking it down in the liver.
This metabolism creates toxic by-products called formaldehyde, formate and formic acid.
These build up, attacking nerves and organs which can lead to blindness, coma and death.
Dr Christopher Morris, a senior lecturer at Newcastle University, said: “Formate, which is the main toxin produced, acts in a similar way to cyanide and stops energy production in cells, and the brain seems to be very vulnerable to this.
“This leads to certain parts of the brain being damaged. The eyes are also directly affected and this can cause blindness which is found in many people exposed to high levels of methanol.”
Of the victims so far, five of the six have been women.
Toxicity from methanol is related to the dose you get and how your body handles it.
As with alcohol, the less you weigh, the more you can be affected by a given amount.
Dr Knut Erik Hovda from Médecins Sans Frontières (MSF), which tracks methanol poisonings, says awareness varies a lot among tourists and healthcare staff in different parts of the world – and that could mean delays in diagnosing it.
“The symptoms are often so vague until you get really sick,” he told the BBC.