A test that uses earwax to measure levels of the stress hormone cortisol could "transform diagnostics and care for millions of people with depression or stress-related conditions", scientists have said.
The researchers believe the test, which can be done at home without clinical supervision, may also have the potential to measure glucose or Covid-19 antibodies that accumulate in earwax.
They say the method is a cheap and effective way to measure chronic cortisol levels, when compared with the other methods such as using hair samples.
While blood, urine and saliva tests can be used to measure cortisol, Dr Andres Herane-Vives, of University College London's Institute of Cognitive Neuroscience, said these samples can only track short-term levels rather than chronic cortisol levels.
Dr Herane-Vives, who is lead researcher on the study published in the journal Heliyon, said: "Cortisol sampling is notoriously difficult, as levels of the hormone can fluctuate, so a sample might not be an accurate reflection of a person's chronic cortisol levels.
"Moreover, sampling methods themselves can induce stress and influence the results.
"But cortisol levels in earwax appear to be more stable, and with our new device, it's easy to take a sample and get it tested quickly, cheaply and effectively."
The testing device, developed by Dr Herane-Vives and his team, resembles a cotton swab but has a brake that stops it from going too far into the ear and causing damage.
The tip contains organic material, with a solution that has been tested to be the most effective and reliable at taking samples, the researchers said.
The pilot study involved an international team of researchers from the UK, Chile and Germany, who recruited 37 study participants to test different cortisol sampling techniques.
The research also analysed hair and blood samples from the same participants.
They found that earwax samples yielded more cortisol than hair samples, and the ear-swabbing technique was the fastest and potentially cheapest method.
Dr Herane-Vives and his team are also investigating whether the device could be used to measure glucose levels from earwax samples, for monitoring of diabetes, and potentially even Covid-19 antibodies.
He added: "After this successful pilot study, if our device holds up to further scrutiny in larger trials, we hope to transform diagnostics and care for millions of people with depression or cortisol-related conditions such as Addison's disease and Cushing syndrome, and potentially numerous other conditions."