Can thermal cameras help spot coronavirus?
As lockdowns ease, thermal imaging cameras are popping up in all sorts of public places to assess the state of people's health.
What do thermal imaging cameras do?
Using infrared technology, thermal cameras detect radiating heat from a body - usually from the forehead - and then estimate core body temperature. These cameras are an extremely powerful tool, often deployed by fire fighters to track smouldering embers and police to search for out-of-sight suspects.
But they are not designed to be medical devices. So how useful are they in the current pandemic?
They can give a reasonable measure of skin temperature, to within half a degree - but that's not the same as body temperature.
"These devices, in general, are less accurate than medical device thermometers like those you stick in the ear," says Derek Hill, professor of medical imaging science from University College London.
What is normal body temperature?
About 37C (98.6F). A high temperature is usually considered to be 38C or over. But normal temperature can vary from person to person and change during the day. It can also fluctuate during a woman's monthly cycle.
Taking an accurate reading of core body temperature isn't easy. Although it can be measured on the forehead, in the mouth, the ear and the armpit, the most accurate way is to take a rectal reading.
Do thermal cameras detect coronavirus?
No, they only measure temperature. A high temperature or fever is just one common symptom of the virus. Others include nausea, headaches, fatigue and loss of taste or smell. But not everyone with the virus gets a high temperature and not everyone with a high temperature is infected with coronavirus.
So thermal cameras alone will miss infected people with other symptoms or no symptoms at all - known as false negatives. They will also identify people unwell with a fever for another reason - known as false positives.
What if I'm wearing a face mask or covering?
"Heat radiating from the skin will likely be impacted by wearing face masks," says Prof Ferryman.
That's why most temperature measurements are based on the forehead, which is usually exposed.
Will I be hotter if I've been exercising?
Not necessarily. Skin temperature actually goes down during exercise as sweat appears on the surface of the skin.
The body is pretty good at regulating its temperature even after exercise, so it would have to be really quite high to show up.