If you are soon travelling abroad, experts are urging vigilance after six tourists recently died, several of them from confirmed methanol poisoning — a nearly invisible killer that’s hard to spot in tainted alcohol.

Methanol is a clear, colourless alcohol used in all kinds of everyday products like industrial cleaners, solvents, paint, cosmetics and anti-freeze. While methanol itself is not harmful, it becomes deadly when consumed, explained Lewis Smith, manager of national projects at the Canada Safety Council.

“When the human body consumes methanol, it transforms it into two different types of chemical compounds in the body; it turns it into formaldehyde and then formic acid. To simplify it, methanol consumption causes the person’s blood to become acidic and that can become fatal very quickly,” he told Global News.

On Nov. 20, Canada issued a travel advisory after six tourists, mostly aged 19 to 20, died from suspected methanol poisoning in a popular backpacker town in northern Laos earlier this month.

“Several foreigners in Vang Vieng have been victims of suspected methanol-adulterated alcohol poisoning,” the warning read. “Be vigilant if you choose to drink alcohol. Avoid accepting free or extremely low-priced drinks. Only buy alcohol in sealed bottles and cans from reputable shops. Seek medical assistance if you begin to feel sick.”

The advisory comes after two Australian teenagers and a British woman died from suspected methanol poisoning after drinking tainted alcohol in Laos. An American man and two Danes also died, though their exact causes of death have not been released. A New Zealander also has been sickened.

Methanol poisoning is a significant health issue in Asia, with outbreaks frequently reported in countries such as Indonesia, India, Cambodia, Vietnam and the Philippines, according to Médecins Sans Frontières.

As authorities continue investigating the circumstances surrounding the deaths of the six foreigners, here’s what Canadians need to know about methanol poisoning.

There are three main types of alcohol: ethanol, methanol and isopropyl. Ethanol is what is found in consumer spirits and is the only one intended for consumption. Isopropanol is the main ingredient in rubbing alcohol and hand sanitizers.

Methanol, commonly called wood alcohol because it is the byproduct of wood distillation, is frequently used as fuel and in products such as antifreeze and solvents.

It has a faint odour similar to alcohol, though the scent is subtle and not very strong. Despite its resemblance to ethanol (the type of alcohol typically found in beverages), methanol is highly toxic, Smith said.

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“It requires such a small dose to become fatal,” he said.

Consuming as little as four millilitres of methanol (close to one teaspoon) can lead to blindness, while ingesting 25 to 90 millilitres (roughly around one shot glass) can be fatal, according to the Methanol Institute.

If you’ve consumed methanol in an alcoholic beverage, it may be difficult to detect at first, Smith said, as the initial symptoms can resemble those of regular intoxication. Drinking the toxic substance causes nausea, vomiting, dizziness and vision problems.

After the initial symptoms of methanol poisoning subside, they typically reappear six to 30 hours later, but with much greater severity, Smith said. This delayed onset is what makes methanol poisoning particularly dangerous, as the effects can worsen rapidly, leading to more serious health complications.

“If methanol is consumed with ethanol, it might even take a few days to see the symptoms,” he said. “When you consume ethanol and methanol at the same time, the ethanol gets processed by the liver first, so the methanol just sits and waits there,” Smith said.

Once the body begins metabolizing the methanol, it turns acidic in the bloodstream, leading to toxic effects.

Because methanol poisoning often goes unnoticed in the early stages due to a latent period between ingestion and toxic effects, the World Health Organization (WHO) warned that victims typically seek medical care late, contributing to high morbidity and mortality rates.

After hours, symptoms like headache, vomiting, abdominal pain and vertigo develop, along with respiratory distress and vision impairment. Severe cases can lead to blindness, coma and death, according to the WHO.

Methanol is often deliberately and illegally added to alcoholic beverages as a cheaper alternative to ethanol in countries where taxes on legitimate alcohol or the cost of legitimate alcohol might be perceived as too high, Smith explained.

“Cheap is the main reason for it. Most drinks have a form of ethanol in them, which is a very safe compound created with corn and wheat. Methanol is hydrogenized carbon monoxide, so obviously it’s much more fatal, not something that we should be consuming,” Smith said. “But it’s cheaper and easier to produce in quantities, especially in countries where alcohol laws and regulations aren’t quite as stringent.”

Some illicitly produced drinks are made to appear legitimate through bottle design and labelling and consumers can be misled into believing that they are buying a genuine brand of alcohol. Bottles may be sold in shops, markets and bars, often at a “bargain price,” according to the Methanol Institute.

This practice is also not specific to Laos or Southeast Asia, but occurs wherever taxes on legitimate alcohol or the cost of legitimate alcohol is perceived as being too high, the WHO warned.

“When we’re talking about treating methanol poisoning, time is of the essence,” Smith said.

“Ideally, it’s treated in a matter of hours because once those symptoms kick in for the second time, it becomes much more difficult to be able to treat it because, at that point, it’s been pushed through the body. The person’s body is now acidic, which can create a whole host of problems,” he said.

Methanol poisoning can be treated effectively if diagnosed within 10 to 30 hours, the Methanol Institute said.

Fomepizole is the preferred treatment for methanol poisoning as it inhibits methanol metabolism, but it may not always be available, the institute said. If fomepizole is not accessible, high doses of ethanol (such as whisky or vodka) can be used instead, as ethanol is processed by the liver first, delaying the toxic effects of methanol.

To protect yourself from methanol poisoning while consuming alcohol during travel, the WHO recommends several key precautions.

First, it said to avoid purchasing or consuming alcohol that is not legally produced or sold, particularly from informal settings like market stalls, where drinks may be offered at suspiciously low prices.

It’s also important to check labels carefully, steering clear of unlabelled containers or bottles with broken seals and being cautious of branded products with poorly printed labels or typographical errors.

According to the Methanol Institute, alcoholic beverages such as canned beer, cider, wine and pre-mixed drinks are generally safer and less prone to mixing with methanol. But the key is to make sure the seal is not broken.

Smith said it’s very important aware of the symptoms of methanol poisoning —such as headache, dizziness, nausea and vision issues — and to seek immediate medical attention if you suspect poisoning.

“If you suspect you’ve been poisoned with methanol or even if you’re unsure of it and you’re not feeling well, it’s such a great idea to seek out medical help,” he said.

–With files from The Associated Press