Image of a cell

Seeing Infection

16 November 2022
Evolution has given us a kind of 'Sick Sense'
Dr Karl talks about our ability to somehow tell if a fellow human is sick, or unwell.
Image of Dr Karl

When I was a junior medical doctor, I was lucky enough to work with some very experienced senior doctors. They had training, skills and experience way beyond mine – and very impressive clinical wisdom.

One very busy day, my boss rang me up. They had only seen the patient across the room, and hadn’t even had the chance to speak to the patient, or know what their complaint was. My boss said, “Something worries me about the look of this person. I want you to do an extremely full and thorough admission.”

The patient looked just fine - actually looking younger than their years. They were super-fit, gave classes in personal fitness, and ate really well. Their one complaint was that when eating, they got full too quickly – even before they got halfway through what used to be a regular-sized meal.

Cancer cells

Cancer cells

They turned out to have a small, but very fast growing, and very nasty, cancer of the stomach – which had already spread too far. Within eight months, they died.

Somehow, my boss had sensed that this person was seriously ill.

Surprisingly, it turns out that many of us can recognise if another person is sick just by looking at their face.

In a recent medical study, a group of Swedish people were infected with bacteria. Then, separate groups of people from different cultures were shown photos of the Swedish volunteer’s faces.

Some of the volunteers had been injected with saltwater, which did nothing – they were the control group. The rest had been injected with the bacterium, E. coli. All of them were photographed twice – just before the injection, and two hours later. By two hours, the people infected with E. coli had the beginnings of a fever – both their temperature and heart rates had risen. And their immune system had well and truly kicked into action. A marker chemical called interleukin-6 had increased from its normal levels of about 4, to nearly 1000. All the Swedish volunteers recovered fully.

Image of a red haired child with a tissue

The people who looked at the photos were three urban groups (Mexico City, Ubon in Thailand, and Stockholm) and three hunter-gatherer groups (Sonoran Desert in Mexico, and two separate groups in the Malay Peninsula – the Maniq and the Jahai).

All that the photo reviewers got were photos of faces, and they were asked to identify anyone who looked sick.

Amazingly, people from all the different groups (covering a huge cultural range) could recognise who the sick people were, in the two-hour photo.

Quite a few animals (especially those that live close together) can detect if one of their group is sick. After all, in a group, an infectious disease can spread very quickly. We know that both ants and chimpanzees will separate out infected individuals from the group – to protect everybody else.

So you might expect humans, being an ultra-social animal, to also have this ability. And this small study seems to back this up. It seems that subtle cues, like a pale face or slightly droopy eyes, can be recognised early on as signs of sickness.

Maybe our supposed sixth sense could be our “sick” sense?

© Karl S. Kruszelnicki Pty Ltd 2022