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Very few people actually enjoy getting poked for a blood test. In fact, it can be a reason some people avoid their physicians altogether.

And that is why scientists are thinking outside the needle to create the next generation of diagnostic tests. And it turns out, various secretions can tell us more about our bodies than you might think, including sweat and tears… and also earwax. But let us start with spit.

When you think of analyzing bodily fluids, blood might be the first one you think about, but spit gives us about the same information and without needles! In fact, saliva has similar components to blood, because it is partly filtered blood plasma. As that fluid rushes around your body, some of it is diverted from the blood into the salivary gland.

Then, the plasma mixes with water in the salivary glands, which then gets into your mouth as saliva. So, like blood, spit has antibodies and enzymes, both of which are hugely valuable in making diagnoses. Antibodies are made by the immune system when it detects viruses, or in autoimmune conditions.

And enzymes are involved in basically every process in your body. How much saliva someone produces, as well as the acidity of their spit, can also be helpful for making diagnoses. From a logistics standpoint, spit is pretty easy to collect compared to blood, as well, and it’s a cheap way to test larger populations without any risk of spreading bloodborne pathogens.

Now, because spit is about 99.5% water, scientists were originally concerned that it was too diluted to be useful. But with advances in technology, tests are more sensitive and are able to pick up on specific molecules at lower concentrations. And that’s come in handy.

Like, saliva testing has been super helpful during the COVID-19 pandemic in some communities. So, scientists can potentially use saliva tests to test larger populations for the presence of the virus or antibodies quickly and cheaply. And that is only the beginning.

Similarly to spit, breath is also something you produce all the time. When you exhale, you release carbon dioxide, but your body also releases volatile organic compounds or VOCs, a huge category of compounds that are able to stay suspended in the air. These volatile compounds are usually generated as byproducts of normal bodily processes.

But the VOCs in our breath also change as our health does. For instance, our bodies make nitric oxide to combat inflammation. So, one way to diagnose patients with chronic inflammation in the airways, like from asthma, is to measure how much nitric oxide they’re breathing out.

Scientists can also trace VOCs to other respiratory conditions like cystic fibrosis and smoking-related conditions. Collecting breath is easy enough. We have special devices for it that are similar to the breathalyzers used to measure blood-alcohol content.

Then, scientists can analyze that breath with gas chromatography or mass spectrometry, two techniques that separate out different kinds of molecules. Now, these techniques are used all the time in research, so they’re not uncommon. But making, like, an “electrical nose” for medicine is still easier said than done.

It’s taken almost 40 years, because collecting samples and standardizing the methods has been challenging. But now, with recently improved sensors, scientists have been able to smell out Parkinson’s disease. Right now, there’s no definitive diagnostic test for this condition.

But in a 2018 study, scientists collected the breath of patients with Parkinson’s symptoms and observed a spike in benzaldehyde, and acetophenone was observed in a slightly higher amount. It’s not clear what’s special about these two compounds. They’re just a part of the spectrum of VOCs normally in our breath.

But if other researchers also notice this pattern, these compounds could be a marker to help diagnose Parkinson’s disease. There’s still a long way to go before electrical noses hit the market, but these results are a step in the right direction. Lots of breathing is sometimes accompanied by lots of sweating, which is our next bodily fluid.

Although we couple sweating with working out or it being hot outside, we actually sweat all the time. So someday, analyzing your sweat could provide doctors with real-time, continuous health monitoring. But for now, most of the studies have focused specifically on exercise.

Apart from a bunch of water, you can find electrolytes, metabolites, and other small molecules like glucose in your sweat. These molecules are circulating in your body all the time, like, electrolytes move nutrients around your cells and also maintain your body’s pH. And because they’re water-soluble, we lose some of them in our sweat.

Meanwhile, other small molecules reach the sweat mainly by diffusion through the sweat glands. And to keep track of them, some scientists are trying to use a battery-free, wireless sensor. A sensor like this could tell you all kinds of things about your body.

Like, the glucose in sweat can be correlated to how much glucose is in your blood. And scientists have taken advantage of that to determine if glucose is present in sweat during exercise. Meanwhile, the levels of electrolytes and pH of sweat can provide information on how hydrated someone is while exercising, and let them know if they need a water break.

Scientists have also tracked lactate. Lactate is generated when you do demanding exercises, like sprinting, in cases where cells aren’t all getting enough oxygen, so some of them start functioning without it. To measure when this switch happens, scientists measure the amount of lactate produced and diffused into the sweat, which could be used as an indicator of physical stress.

All of these physiological aspects in conjunction give a well-rounded view of someone’s body while exercising. Another bodily fluid that doesn’t involve needles is tears. Like sweat, we produce tears all the time, but they mostly get drained into the nose.

That doesn’t mean, though, that we cannot learn from them. So, tears are mostly made out of water and salt. But there’s also more to them.

Like saliva, tears have a composition that’s pretty similar to blood. They form from blood plasma that gets filtered through the lacrimal glands. So they’re an excellent candidate for testing for things you might otherwise look for in blood.

For example, the amount of glucose in tears can be correlated to the amount in blood, making it a great candidate for folks with diabetes who want to minimize needles. To harness this property, scientists designed special contact lenses with sensors. Having sensors on your eyeball might not sound like a fun time, but the sensors are embedded in something called hydrogel, a kind of polymer that’s soft and squishy like gelatin, so it’s more like a regular contact lens.

That helps with comfort, but it’s also why these contacts work. If the sensors in the lens sense any glucose around, the gel will shrink or swell. And as it does, light will travel through it differently, so the contact lens will actually change color.

As glucose concentration increases, you can see the color changing from green, to blue, and then to yellow-red. Fancy contact lenses aren’t the only application here, though. Other scientists are directly collecting tears to diagnose breast cancer.

The technology is called TearExo, and in it, researchers use a glass chip with an antibody that detects cancer exosomes. Exosomes are little packages that are secreted and passed on to other cells. They often carry proteins, and different types of RNA and DNA used to exchange information between cells.

It’s like contactless pickup. Food in a bag arrives at your door, and then you bring it into your home cell. Exosomes from cancer cells also have multiple membrane proteins that aren’t found in normal vesicles.

So If the exosomes from cancer cells are present in the tears, the device will recognize those proteins and tell you in 10 minutes. Finally, most of these techniques so far show us a snapshot in time. But what if a doctor wants to know something about your health from last month?

Well, there’s an often-overlooked secretion that can tell you just that… earwax! In 2017, it was found that earwax can say a lot about you, from the food you’ve eaten to exposure to environmental pollutants. That’s because similarly to other secretions, earwax contains volatile organic compounds.

Here, they’re trapped in the oils that form the wax, and can be analyzed in a similar way to the VOCs in your breath. But the big differences are that earwax accumulates over time, storing up a record of VOCs. Also, since the earwax is snuggled in the ear canal, it’s protected from other contaminants like perfume, sweat, or cosmetics.

So, earwax has been used to diagnose metabolic disorders even before traditional techniques. And these are just some of the overlooked secretions that can tell you a lot about your body, no poking required. And if research keeps going like this, these tests might be the norm in the future.

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