Blood, sweat, tears: what do they say about you? Scientists and doctors have long turned to body fluids for clues about our health, but now they’re finding that they can reveal more about the hidden workings of our bodies than once realised – and what’s more, it’s becoming ever-easier to test them ourselves.
Last week, for instance, BBC Future covered the story of a Star Trek-like tricorder that promises to diagnose fatal diseases like Ebola before people are even aware they’re infected, and without them needing to travel long distances. Watch the video below to find out more:
It’s not the only technology that allows for complex testing outside hospitals either: devices like the Cue are being marketed that will enable self-testing for fertility, flu and signs of inflammation. And the X-Prize Foundation is currently running a prize to discover the next generation of medical tricorders, capable of diagnosing various illnesses.
The next five to 10 years is expected to yield many more such tests, as well as the recruitment of new sources of information – including some our more embarrassing excretions.
As you might expect, many of these kits will involve the testing of blood. “In blood you can detect just about everything that you’ve eaten, or that’s going on in your body,” says Guy Carpenter, reader in oral biology at Kings College London.
But it’s possible that technology will emerge to measure other excretions, says George Preti at the Monell Chemical Senses Center in Philadelphia. He is currently investigating what your earwax can say about you. Unlike blood, earwax is a fatty substance, which means certain molecules may concentrate there and be easier to detect than in more watery fluids. “If you have a certain group of metabolites that like to dissolve in lipids (fats), we may be able to look at them in earwax,” Preti says.
For example, maple syrup urine disorder, a genetic condition in which people can’t break down certain parts of proteins, can be diagnosed by sniffing earwax: “It smells of maple syrup,” says Preti. He recently published research revealing that the earwax of people of East Asian descent smells different to that of European, African or American descent, as does their body odour. “We already have an indication that there is some disease-related information in earwax; there’s also information about where you’ve been and what you’ve eaten.” Whether earwax will turn out to be more useful than blood and other body fluids for diagnosing certain conditions remains to be seen, but “we don’t know unless we investigate it,” Preti points out.
Then there’s sweat. For decades it has been used to screen newborns for cystic fibrosis, which alters the balance of sodium and chloride in their sweat. Now, wearable patches are being developed that could alert athletes to changes in the balance of electrolytes that might signal that they’re about to “crash” because of dehydration or physical exertion. One advantage of monitoring sweat is that it could be done passively – you don’t have to stick yourself with a needle, or even mess about with swabs – an electronic sweat-sensor could be worn under clothing that transmits information wirelessly, without you even having to think about it.
But there may also be limitations. “Sweat contains marker molecules, but they are very, very variable, which will probably preclude their direct clinical use,” cautions Jeremy Nicholson, chair in biological chemistry at Imperial College London. Its composition is also influenced by the activity of microbes living on our skin. Blood, on the other hand, tends to provide a more accurate picture of what’s happening inside the body, as it infiltrates every tissue, and the body keeps its basic composition in strict check.
Even within a drop of blood, there’s still a great deal more information that might be gleaned than is currently possible. For instance, Manfred Kayser at Erasmus University Medical Centre in the Netherlands is currently developing new DNA tests that might enable a person’s age, physical appearance, and geographic origin, to be predicted from a blood sample, which could help police identify criminal suspects or badly decomposed bodies.
Some of the greatest excitement surrounds the potential predictive power of the micro-organisms living within and upon us. “We think that at least a third of the metabolites in our blood are being produced by our microbes,” says Tim Spector, professor of genetic epidemiology at Kings College London and author of The Diet Myth. And it’s becoming apparent that they are influencing our health in hitherto unimaginable ways. For instance, the mood-altering chemical serotonin isn’t only produced by your brain cells; it turns out that certain gut bacteria produce it too, and they may therefore play a role in depression.
The best place to look for changes in your bacterial flora though, is poo. “If you gave me your poo sample and your DNA sample, I’d be able to tell much more about you from your poo than your DNA,” says Spector. This is because although the genes of any two people are approximately 99.9% similar, we only have 10-20% of our microbes in common. And recent research suggests the type of microbes in our guts – and therefore our poo – are influenced by what we eat, and where we’ve been living. “We can identify the differences between Europeans, Africans and South Americans, and we have some early data from twins showing differences between those who live in Scotland and those that live in England,” Spector says.
Not only could analysing our poo for microbes and the chemicals they produce help tease apart complex diseases like depression and obesity and diabetes, it could also provide an early warning that an elderly person is becoming dangerously frail and needs additional support. “As elderly people go downhill, they have a marked rise in certain gut microbes, or a lack of others,” says Spector.
As these new sources of information mature, and the cost of analysis decreases, more self-testing kits are inevitable. Some believe this will democratise healthcare, reducing the need for people to travel, and enabling them to monitor and take greater responsibility for their own health. But it could also result in unnecessary worry and false leads. “We can give people tests for various things, but the interpretation of those tests will still require the guidance of a health professional,” Carpenter points out. Issues of privacy may also come to the fore. For now at least, few of us pay much regard to what happens to our secretions and emanations once they leave our bodies.
Yet for better or worse, soon a small sample of your blood, sweat, and even your earwax will be all that’s necessary to reveal a great deal about your behaviour, health and more.