Scientists have mapped how sensitive different parts of the human body are to pain.
Experiments testing how well people can identify where on their body they've been touched are routine, but the equivalent for pain has never been assessed before.
"We don't know much about pain," says Dr Giandomenico Iannetti of the UCL Department of Neuroscience, Physiology and Pharmacology, whose lab the research took place in.
That's because to study a sensory system you need to be able to isolate the input, in this case pain, from other inputs like touch. This is especially important because touch is actually a pretty effective painkiller (that's why you rub your knee after you fall on it).
It's been difficult to find stimuli that provide pure pain without touch. Until a pair of high-powered lasers came along.
So I went to visit the lab at UCL to see just how much pain these lasers could inflict. This was the set up.
There were two lasers pointing down to where journalists were going to put their hands. The wires lead off to a dial that the scientists used to decide how much they want to hurt you. Everyone in the room had to wear safety goggles. Selfies were tolerated, but not encouraged.
(This set up wasn't exactly the same as it was for the volunteers who participated in the study. They wore blindfolds, for example, so they couldn't tell if one or two lasers were activated at any one time.)
The lasers in this experiment allowed the researchers to trigger two types of pain.
When something happens to trigger pain, there are two pathways the signal takes to travel from your skin to your brain. The first is quicker and causes you to feel a sharp stinging pain, a bit like a pinprick. The second pathway causes a dull burning sensation that lasts longer.
This is my face before the scientists even turned the lasers on.
"Oh, is that it?"
And... it does kind of hurt more the next time.
In the actual study, pain was inflicted on 26 volunteers using lasers and the volunteers' sensitivity on different parts of their bodies was measured.
Here's the full map, based on data from the research paper.
Eventually the results should be able to help people with chronic pain.
Almost ten million people in the UK suffer pain almost daily.
Teaching chronic pain patients how to differentiate between two points of pain could form part of the treatment for some chronic pain conditions. "There's some soft evidence that doing it in the tactile field can help with complex regional pain syndrome, one of the rare pain syndromes that is very difficult to treat," says Dr Roman Cregg, who treats patients and was not involved in the research.
The laser technique could also allow doctors to monitor nerve damage, a common cause of chronic pain, across the body, giving them a quantitative way to see if a condition is getting better or worse. "I'm excited about the prospect of taking this to the clinic," says Dr Cregg.