At least six tourists who traveled to Laos have died in recent days, prompting international alarm about the dangers of consuming alcoholic drinks that contain methanol.

A fifth person, identified as a British woman, has died in connection with a mass alcohol poisoning incident at a tourist spot in Laos, the British government confirmed Thursday.

The US State Department issued a warning to travelers to be “alert to the potential risk of methanol poisoning.” But what is methanol, and how do you avoid it?