In 1783, the Icelandic fissure volcano Laki erupted. One in five Icelanders perished, partly because most of their livestock died in the eruption’s aftermath, but also because of direct effects from the geochemistry of the lava. The effects spread to much of continental Europe, but with less gruesome results. There are many archival reports of the presence of a bluish-grey haze or “dry fog” and an acrid smell to the air – probably high sulphur dioxide levels. There was an increase in mortality in Europe too, with 25 % more deaths over and above the annual norm in France, possibly exacerbated by the fog’s coincidence with a scorching summer. The politician-scientist Benjamin Franklin was the first to make the connection between news of the eruption, atmospheric oddities and spectacular sunsets. The spread of volcanic emissions far and wide at the surface can be put down to the relatively quiet effusion of lava from Laki; explosive eruptions generally jet gases and ash upwards to reach the stratosphere. The principal killing agent was the fluorine-rich nature of the gas and ash from Laki, which induced a rapid onset of bone-diseases in humans and livestock alike. That is something special to Icelandic magmatism, the only significant above-sea level part of a mid-ocean ridge system. However, fluorine compounds commonly occur in some volcanic ashes, and mortality spread beyond the immediate effects of volcanism is a major threat. Currently, archaeologists and pathologists are exhuming burials from the time of Laki’s last known killer eruption to seek statistics on the influence of fluorosis in its human victims (Stone, R. 2004. Iceland’s doomsday scenario? Science, v. 306, p. 1278-1281). The signs are bony nodules and spiky fibres that fluorine ingestion, most disastrously from water, produces. Early results reveal many skeletons with clear malformation. Fluorosis leads to a hugely painful and lingering death. Usually it results from a slow build-up of fluorine from contaminated water in areas that are rarely associated with active volcanism. The clearest sign of its onset is a brownish mottling of children’s teeth, and it is easily remedied by changing the water supply. Delivered massively and suddenly, as it was in late 18th century Iceland, gave little chance to its victims. A recurrence would possible be just as disastrous today.