Professor Brian Cox has documented his journey inside a dangerous cave, and it’s somewhere you might want to avoid as your next vacation spot.
Known for roaming to unusual corners of the world, Cox has explored plenty of strange environments — but this one ranks among his most unsettling.
Most of the time, the physicist is guiding viewers through big scientific ideas, whether that’s explaining the speed of light or unpacking how the universe behaves.
This time, though, he stepped into a place where the conditions feel actively incompatible with human life.
In the Mexican city of Tabasco, Cox ventured into the dark, hazardous, and oddly compelling ‘Cueva de Villa Luz’ (translated to mean the cave of the house of light).
And while caves can be intimidating on their own, this one comes with an added threat: bacteria and gases so dangerous to people that entering becomes a serious risk.
Yet for the creatures adapted to it — including its pink fish and a single-celled extremophile-like bacteria known as ‘Snottites’ — the cave functions as a busy, thriving ecosystem.
Cox documented the experience during his BBC Earth Science adventure on the Wonders Of The Solar System show, showing how the cave’s chemistry challenges the humans inside while supporting the microbes around them.
He described it as ‘the definition of a hostile environment’, largely because it’s ‘full of hydrogen sulfide gas’, a colorless, highly flammable gas often recognized by its eggy smell.
Because of the gas, Cox said the team had to take multiple precautions: protecting equipment that could be damaged by the acidic atmosphere, wearing a mask, and using a monitor to track which sections of the cave contained higher or lower concentrations.
Hydrogen sulfide exposure can cause serious health effects. The Illinois Department of Public Health lists ‘fatigue, loss of appetite, headaches, irritability, poor memory and dizziness’ among possible symptoms.
At sufficiently high levels, the gas can also be lethal after only a couple of breaths.
But while Cox and the crew had to treat every step carefully, the ‘Snottites’ he came to see are adapted for the extreme conditions and can flourish there.
As Cox put it, the ‘guys breathe in hydrogen sulfide and oxygen and produce sulfuric acid’, which is how they earned the name ‘Snottites’.
The microbes generate sulfuric acid as a metabolic byproduct, forming biofilms that coat the cave walls in a thick, snot-like layer — and that process speeds up the corrosion of limestone.
It’s also capable of harming human skin, which is why contact is strongly best avoided.
“One type of biofilm, called a snottite because of its appearance, has a pH of zero or one,” said Daniel S. Jones, graduate student in geosciences told Penn State University. “This is very, very acidic.”
Even so, Cox appeared unfazed: he handled a pH dip stick without gloves, collected a sample of biofilm, and noted it was as ‘strong as battery acid’, describing the ‘Snottites’ as a ‘strange organism’.
Given what’s living — and circulating — in that cave, it’s hard to argue.