Nausea and vomiting are common after surgery, but wearing noise-cancelling headphones during the procedure helps prevent these unpleasant side effects. This simple intervention also supports the idea that our brain processes sounds even when we’re not consciously aware of our surroundings.

“That data is really encouraging and is actually in line with decades of research showing that anaesthesia is not simply an off switch,” says at the Baylor College of Medicine in Houston.

Nausea and vomiting are common side effects of anaesthetics. Patients are routinely given drugs to prevent them, but at the First Affiliated Hospital of Soochow University in Suzhou, China, and his colleagues wanted to investigate a non-pharmacological approach and presented their results at the Anesthesiology conference in San Diego.

The team recruited 192 patients who had keyhole gynaecological surgery under general anaesthesic. Half were randomly assigned noise-blocking ear defenders, which they wore from the start of anaesthesia until the end of surgery. All the patients received standard anaesthesia and anti-nausea medication.

Free newsletter

Sign up to Health Check

Sign up to newsletter

Within 48 hours of the surgery, 35 per cent of those wearing ear defenders experienced nausea or vomiting, compared with 52 per cent of those without them. The researchers also found that symptoms were less severe among those whose hearing had been protected, defined as the patients vomiting less and it having less of an impact on their daily life.

Operating theatres aren’t generally quiet places, with Liu recording average noise levels of 66 decibels – around the level of a normal conversation – during the study.

The relationship between sound, nausea and vomiting, and anaesthesia is unclear. However, the latter affects the nervous system, and noise is thought to trigger a stress response that activates the autonomic nervous system. This helps regulate involuntary bodily functions, such as heart rate, and interacts with the brainstem pathways involved in nausea and vomiting.

Hearing loss is bad for the whole body – but new treatments are coming

From dementia to heart attacks, hearing loss has been linked to a wide range of effects across the body, and the condition is on the rise. Fortunately, we’re learning how best to safeguard this crucial sense and how we might be able to reverse the damage

However, Liu stresses that the researchers didn’t look into the mechanism behind how ear defenders prevent nausea and vomiting, so the idea of them dampening this response “remains a hypothesis”.

Nevertheless, the results tell us more about brain activity under anaesthesia. “The biological plausibility is that general anaesthesia produces unconsciousness without necessarily eliminating all neural processing of sound,” says Liu.

Liu hopes to one day conduct a larger trial at multiple locations that measures noise exposure relative to nervous system activity among patients under general anaesthetic.

A quarter of active-duty male soldiers in the US Army have low testosterone, according to a study of nearly 500 personnel. This has implications for the recent that all US service members aged 30 and older must undergo annual testosterone screening and be offered voluntary replacement therapy if they have low levels.

“For soldiers with genuine, symptomatic testosterone deficiency, appropriate treatment can improve symptoms and important aspects of physical health, including sexual function, body composition, muscle mass and bone health,” says at the University of Melbourne, who wasn’t involved in the research. “However, there is currently insufficient evidence that [it] will improve military readiness, operational performance or fighting capacity.”

at Pennington Biomedical Research Center in Louisiana and his colleagues analysed data from the , which measured testosterone levels and other health markers in active-duty personnel at five military centres across the US between 2024 and 2026.

Among the 479 male personnel tested, 26 per cent had testosterone levels below 300 nanograms per decilitre, classified as low by the . Based on this, the researchers estimate that 100,691 male soldiers in the US Army could have low testosterone readings.

Older male personnel were more likely to have low testosterone, with 33 per cent of those aged 30 and older being classified in this group. Female personnel weren’t included in the analysis because their testosterone levels were often below the limits of detection.

Free newsletter

Sign up to Health Check

Sign up to newsletter

When the testosterone-boosting initiative in July, Pete Hegseth, the US defence secretary, noted that testosterone levels naturally decline with age and said the decision to offer replacement therapy to soldiers with low levels was “about restoring and optimising your natural capabilities, protecting your longevity, ensuring you have the biological foundation required to sustain the fight”. There are no ramifications for choosing not to have the therapy, he said, adding that personnel under the age of 30 will also be able to opt for testosterone screening.

But a single testosterone test isn’t a reliable measure of deficiency, says Katz. “Testosterone levels can fluctuate considerably, even within the same individual, and may be influenced by numerous factors, including the time of day blood is collected, recent food intake, inadequate sleep, obesity, acute illness and excessive physical or psychological stress,” he says.

Even if testosterone levels are consistently low in blood tests, that doesn’t necessarily mean someone has a deficiency, says Katz. The American Urological Association that a clinical diagnosis be made only if an individual also has related symptoms, such as reduced energy, motivation, libido and erectile function.

Low testosterone levels may protect women from kidney injury

Men get acute kidney injury – where kidney performance suddenly declines – at a higher rate than women. An experiment with mice suggests that this could be related to having higher levels of testosterone

“Testosterone should be prescribed to treat a medical condition, not simply to achieve a higher number on a blood test or as a general strategy to enhance the performance of otherwise healthy soldiers,” says Katz. “I would favour a more targeted approach [to diagnosing and treating testosterone deficiency] based on symptoms, clinical findings and relevant risk factors rather than automatically screening every man over the age of 30.”

Some of the side effects of testosterone replacement therapy include acne, testicle shrinkage and reduced sperm production and fertility. It also increases the risk of (blood clots in the lungs) in older men.

at the University of Queensland in Australia says there is a risk that high testosterone levels will be conflated with being a good soldier. “Testosterone is already increasingly being used as an oversimplified proxy for masculinity and virility,” he says.

Microplastics generated potentially harmful molecules when they contacted serum from blood in a lab experiment. This is due to their large surface area enabling such reactions. If this effect occurs within our bodies, it could explain why they have been linked to cell damage and other health concerns.

Several recent studies have linked microplastics, which form when plastics degrade in the environment, to issues such as poor cognition and cardiovascular disease. This seems to be related to the production of destructive molecules called reactive oxygen species, says at Columbia University in New York. These can then react with different molecules inside cells, contributing to issues like inflammation.

But the extent to which common plastics could be causing such problems was unclear. They don’t always contain oxygen and are therefore not thought to be particularly reactive. “From a pure chemistry point of view, this should be inert,” says Min.

To find out, Min and his colleagues studied the microparticles of a range of commonly used plastics – including polystyrene, polyethylene and polypropylene – and found that “water is a key player” in their effects.

They used techniques including fluorescence microscopy and electron spin resonance spectroscopy to show that a type of reactive oxygen species called hydroxyl radicals spontaneously forms at the surface between plastic and water, making the latter “not regular water anymore”, he says.

The team also showed that this effect is linked to electric charges forming at this plastic-water interface. These charges may help strip electrons from OH- ions in water, generating volatile hydroxyl radicals, says Min.

Free newsletter

Sign up to Health Check

Sign up to newsletter

In experiments, this electric charge attracted biological molecules such as DNA to the surface of microplastics when suspended in water, which appeared to damage both proteins and red blood cells.

The researchers also tested whether hydroxyl radicals were generated when the microparticles were suspended in serum from blood. The effect was weaker, but “still detectable”, says Min. Microplastics have been , however, signals of their presence throughout our bodies and false positive results.

If microplastics do enter our blood, laboratory studies have linked them to cellular , all of which can be caused by reactive oxygen species.

The findings could help explain how those molecules are being produced, says Min, although he adds that the potential size of the effect is unclear and other mechanisms could be involved. It may also depend on whether microplastics are disposed of by our bodies. “How much plastic is in a regular human being?” he says. “We have no idea right now.”

at the New Jersey Institute of Technology says the results are “very important”, and although they don’t directly answer how dangerous microplastics might be, they “provide a starting point” to help us understand the interaction between microplastics and cells.

at the University of New Mexico describes the results as a “critical building block” for this understanding. The surface area of microplastics is probably key to their effects, he says, pointing out that a half-centimetre ball of plastic could degrade into a quadrillion 50-nanometre microparticles, increasing its surface area 100,000 times.

That isn’t necessarily as worrying as it sounds, however. “I encourage people to take a deep breath,” says Campen.

How worried should you be about microplastics?

Microplastics have been found accumulating everywhere from our water to our body tissues, but many of the claims have come under fresh scrutiny. Chelsea Whyte cuts through the research to tell you whether you really need to worry

When the researchers added a surfactant – a chemical that weakens the forces holding the water molecules together – radical generation was dampened. Some lipids act as surfactants in the body. “Microplastics hit your lung and they are surrounded by surfactants immediately,” says Campen. “In most situations that I can imagine in a biological system, they will be surrounded by those lipids. The big concern is [whether] this is getting worse over time, and we really need to get a handle on what the health effects are, or could be, so that we can avoid exposures.”

The findings could also help scientists design safer materials, says Min. The researchers found that the most hydrophobic (water-repelling) plastics they tested, such as polyethylene and polypropylene, showed stronger radical-generating activity than more hydrophilic ones, such as PET (polyethylene terephthalate).

Campen notes, however, that the plastics with the lowest activity are also probably the ones that break down more slowly in the environment. “How do you make that trade off?”