Saliva. Mucous. Blood. With the current pandemic in full swing, our bodily fluids have never been under such close scrutiny.
As a biomedical scientist I'm no stranger to various human secretions. Indeed I have quite the collection of strangers' blood and saliva in my lab. Why? Because these samples can tell us a whole lot about someone's health.
The human body is a finely tuned machine, and all of our bodily fluids, be it blood, urine, saliva or sweat, have their own unique composition.
Each one is a complex mixture of ingredients - cells, proteins, enzymes, electrolytes etc. - all of which are usually found at certain concentrations.
Changes in these levels, or finding unusual components, can tell us that something is going wrong with one of our body systems.
Blood is the most commonly used type of sample in clinical testing. Blood samples can tell us a lot.
We can count the different types of blood cells and figure out whether someone has an infection, a blood disorder or leukaemia.
We can examine which proteins are present, and at what levels, and get information about the function of a patient's liver, or pancreas, or other organs.
We can even identify what antibodies are present, and tell which pathogens people have been exposed to in the past.
Urine is also very useful - as well as being less invasive to collect. Great for gathering information about kidney function, and for diagnosing things like bladder infections.
Also useful for measuring hormone levels - like the hormone human chorionic gonadotropin, which is what is detected in pregnancy tests.
It's not often you go to the doctor and they ask you to give a saliva sample, but these can also be useful. We often use these in our lab to look at levels of hormones, like the stress hormone cortisol, and for molecules that are related to inflammation.
And of course at the moment saliva samples are being used for diagnosis of infection with the SARS-CoV-2 virus.
Less used, but no less important, are other fluids like cerebrospinal fluid and sweat. Fun fact - a sweat test can be used to detect cystic fibrosis, as people with this disorder have much higher levels of chloride in their sweat than usual.
Once you get past the "icky" factor, it's quite fascinating to think just how much we can learn about a person from a few millilitres of blood, sweat ... or even tears.
- Dr Mary McMillan is a lecturer at the School of Science and Technology, University of New England