When you fall asleep, your brain doesn’t just switch off. As the cognitive lights go out, housekeeping begins. Along the outer walls of blood vessels, microscopic currents flow, sweeping away waste that would otherwise cause harm.

This is the glymphatic system, a network of channels that helps the brain clear unwanted proteins and by-products of cellular metabolism. It may explain one of life’s most familiar pleasures: feeling refreshed after a good night’s sleep. Yet we only learned of its existence in 2012, and ever since, researchers have been scrambling to figure out exactly how it works.

Now, it seems this overlooked system may be crucial for our health – when clearance falters, it may contribute to Alzheimer’s and Parkinson’s disease, and possibly other hard-to-treat conditions, including migraine.

Doctors are eager to intervene, wondering whether boosting this nocturnal detox could slow or even prevent disease. “The field is filled with promise, and we’re just starting to do the studies that will find out if it’s going to make good on that promise,” says neuroscientist Jeffrey Iliff at the University of Washington in Seattle. Experiments range from using drugs and red-light therapy to inhaling bursts of carbon dioxide. There’s also talk of improving brain clearance by changing how we exercise or breathe, or even the position in which we sleep. Meanwhile, emerging techniques hint that we might already be able to gauge the health of our glymphatic system using a simple smartwatch.

Yet the young field has already been dogged by disputed methods, exaggerated headlines and the apparent detention of a key researcher. With so much at stake, it is vital to separate promise from hype, establishing what we can reliably measure, which interventions help clear the waste and whether doing so improves our health and prevents disease.

All our cells produce unwanted chemicals that become harmful if they build up. Luckily, we have an elaborate network of tubes called the lymphatic system that runs throughout the body, collecting fluid from cells, filtering it and sending it to the blood, with waste being expelled by the liver and kidneys.

The strange thing is that there are no lymph vessels in the brain. The implication was that the brain’s waste molecules left passively, drifting through the extracellular fluid surrounding brain cells. But this never made much sense for such an energy-hungry – and therefore heavily waste-creating – organ.

A breakthrough came in 2012, when Iliff and his colleagues injected a fluorescent tracer into the brains of living mice. They targeted the subarachnoid space, a thin region between two of the membranes, or meninges, that encase the brain and spinal cord. The tracers rapidly moved from this space into the brain itself. But they didn’t travel through tubes to do so. Instead, they moved along the outside of small arteries, later leaving the brain along the outer layers of small veins. The brain, it turned out, had a waste-disposal system after all – but it was unlike anything we had seen before.

Closer inspection showed that brain cells called astrocytes, which have long, branch-like projections called endfeet, were wrapped around the blood vessels. The tracer chemicals were moving in the narrow space between the astrocyte endfeet and the outer walls of the blood vessels.

Astrocytes belong to a larger group of brain cells called glial cells, inspiring the name glial lymphatic system, or glymphatic system for short.

Three years later, two groups discovered lymph vessels hidden in the meninges. Another part of the puzzle fell into place: the glymphatic system moves waste out of brain tissue, while the newly discovered lymph vessels take it away from there.

Mapping the glymphatic system was only the start, though: researchers also wanted to know what governs its flow. One vital clue came from the activity that occupies a third of our lives.

Why sleep is key to cleaning the brain

In 2013, Maiken Nedergaard at the University of Rochester in New York state and her team, which included Iliff, injected a green tracer into the cerebrospinal fluid of sleeping mice and watched it stream around the brain. After the mice were gently woken, this flow fell by about 95 per cent. The researchers also showed that beta-amyloid, a key waste product associated with Alzheimer’s disease, was cleared roughly twice as fast when the mice were asleep.

Then last year, Natalie Hauglund, a sleep scientist now at the University of Oxford, and her colleagues helped identify a control mechanism. Studying mice, they showed that concentrations of the neurotransmitter noradrenaline rose and fell about every 50 seconds during non-REM sleep. This caused arteries in the brain to alternately swell and constrict, gently pumping the fluid along the outside.

That mechanism could be key to why glymphatic function declines with age. “As you get older, your arteries become stiffer,” says Roslyn Bill at Aston University in Birmingham, UK. “So, I think that whole mechanism probably breaks down.”

Crucially, Geir Ringstad and Per Kristian Eide at the University of Oslo in Norway demonstrated that the glymphatic system also operates similarly in the human brain and that just one night without sleep is enough to reduce the removal of a tracer from people’s brains.

This was one of the first hints that the glymphatic system can go wrong overnight, but what happens when the brain’s housekeeping falters over months or years?

The strongest links between a faulty glymphatic system and disease concern Alzheimer’s. In people with this form of dementia, beta-amyloid accumulates into distinctive plaques, while abnormal tangles of another protein called tau form inside brain cells.

In 2016, researchers including Nedergaard found there was reduced glymphatic transport in mouse models of Alzheimer’s even before amyloid plaques formed. The implication was that impaired glymphatic clearance might allow beta-amyloid to accumulate in the brain, contributing to disease. Since then, evidence has grown that the glymphatic system transports these proteins in people too – this January, Iliff and his colleagues reported that it helps clear beta-amyloid and tau from the brains of people without dementia.

It isn’t just Alzheimer’s that’s in the crosshairs, though. A study last year found reduced glymphatic clearance in the brains of people with early psychosis compared with controls. Other researchers have found links between poor glymphatic functioning and Parkinson’s, migraine, major depressive disorder and post-stroke cognitive impairment. Together, these two studies offer some of the most tantalising signs that we may be able to boost clearance in people – although whether doing so protects their brain health is still unknown.

Of course, a note of caution is needed. These links don’t necessarily mean it is the glymphatic dysfunction that’s causing these conditions, says Iliff. For one thing, the conditions themselves could disrupt glymphatic clearance.

There’s also another possible problem. Many human studies assess glymphatic function using a form of MRI called DTI-ALPS, which tracks the movement of water in the brain, and whose ability to capture glymphatic activity is disputed. In February, Ringstad, Eide and their colleagues compared it with their tracer methods – and found little correlation.

“You have a big part of the field running away with a technique that is invalid,” says Iliff.

No method is perfect, certainly. Even the tracer techniques don’t directly measure the clearance of actual waste chemicals. That said, connections between glymphatic problems and certain conditions seem likely to hold. “There are several diseases where it’s very likely that the glymphatic system could be an important factor,” says Hauglund. “What characterises a lot of these is that they’re very slowly progressing, and that there’s probably a lot happening in the brain before we really see an effect of it.”

Boosting glymphatic clearance in the brain

In theory, then, we may be able to intervene to ensure people’s glymphatic systems work better to prevent such conditions. While there’s currently no approved treatment that does so, several interventions are being explored.

One uses near-infrared light, which is invisible to the naked eye but can penetrate flesh and bone, reaching deep into the brain, where it alters cellular functions and affects pathways involved in inflammation and vascular function. A 2022 review described evidence from animal experiments that transcranial near-infrared light could help treat neurodegenerative conditions, possibly by changing the shape of blood vessels and astrocytes to improve glymphatic flow. However, “we do not yet know that near-infrared light directly increases glymphatic flow in humans”, says Bill.

There are hints it might. In one study, 57 people who had been diagnosed with or showed symptoms of dementia wore a near-infrared light helmet for 6 minutes twice daily for eight weeks and showed some small cognitive improvements. One participant saw an 80 per cent improvement in their ability to draw a clock, for example, while others showed better learning and memory. Results varied considerably across the group, though, leaving uncertainty about how well the treatment works.

Another pilot study tested a headset developed by Canadian company Vielight, which delivers near-infrared light to the brain through the skull and nose. After 12 weeks of regular use, the five participants showed improvements in cognitive tests, while caregivers reported better sleep and less anxiety. But with no placebo group and a larger trial suspended because of recruitment difficulties, the evidence is still too thin to justify buying your own red-light therapy device for home use.

Another approach uses focused ultrasound with microbubbles. Researchers inject tiny bubbles into a vein, where they travel to the brain. Focused ultrasound waves are aimed at the head, which causes the microbubbles to vibrate, jostling blood vessels, changing the flow of glymphatic fluids around them. In mice, this can accelerate the removal of beta-amyloid from the brain.

Meanwhile, Sephira Ryman at the University of New Mexico in Albuquerque has been experimenting with a different way to get brain vessels pumping – carbon dioxide. If people alternate between inhaling high doses of CO2 for about 30 seconds and breathing normal air, it seems to improve the clearance of harmful proteins from the brain. The extra CO2 causes blood vessels in the brain to widen, while switching back to regular air allows them to narrow, thus generating the pumping motion needed for glymphatic function – echoing what happens during sleep.

This isn’t safe to try at home: inhaling CO2 is extremely dangerous. However, when carried out under the watchful eye of Ryman and her colleagues, this simple technique can help remove alpha-synuclein, a protein that seems to contribute to Parkinson’s. At a conference in July, Ryman reported similar findings for beta-amyloid. Together, they offer some of the most tantalising signs that we may be able to boost clearance in people – although whether doing so protects their brain health is still unknown.

Ultimately, Bill would like to develop “a statin for the brain”: a medication that would enhance the blood vessel-driven pumping in older people. “You could take a pill before you went to bed and open up your sluice gates, and the fluid would flow away,” she says.

A study published in March, which Iliff worked on, hints at this possibility. Older adults without any brain-related conditions received the drugs midodrine and dexmedetomidine, which increase the pulsing of blood vessels in the brain. During a single sleep, clearance of tau and beta-amyloid increased by about 10 per cent – although the findings await peer review.

Controversial detox surgery

Elsewhere, enthusiasm for brain clearance may have outpaced the evidence. When it comes to removing waste, the glymphatic system isn’t the only game in town, and work relating to a second, better-known drainage system has recently come under some heat.

Some waste can reach the cerebrospinal fluid that bathes cavities deep in the brain and the meninges that surround it. From there, it can flow out into lymph vessels in the head and neck. Clinicians in China have seized on this mechanism, developing a surgical procedure called deep cervical lymphovenous anastomosis to connect lymph nodes in the neck to nearby veins, encouraging faster drainage. They claim this has significantly improved symptoms in people with Alzheimer’s. However, some researchers have highlighted the limited evidence, small sample sizes and a lack of randomised controlled trials – and have flagged concerns over performing expensive, experimental surgery on vulnerable people. “When I first heard of this treatment, I was shocked,” Steven Proulx at the University of Bern in Switzerland told  in July. “There is basically no evidence supporting this.”

Chinese authorities have now banned the operation outside clinical trials and appear to have detained its inventor, microsurgeon Qingping Xie, although no criminal charges have been announced.

Even setting aside this specific controversy, treating neurodegenerative conditions by boosting brain clearance is problematic, says Hauglund. All such conditions are poorly understood, she says, and now we are trying to treat them by intervening in a system that we also don’t understand very well.

Naturally, that uncertainty hasn’t stopped social media filling with claims about ways to detox your brain, from yogic breathing to sleeping positions. But beneath the hype is a reasonable question – is there anything we can do ourselves to help flush out the waste?

Deep-cleaning the brain at home

When it comes to home-based remedies, most research has focused on exercise, known to have extraordinary benefits for brain health. “Exercise has profound effects on the brain through cardiovascular fitness, cerebral blood flow, metabolism, inflammation, insulin sensitivity and neuronal plasticity,” says Bill. Glymphatic transport may be another part of that picture.

A 2025 study of 37 adults found that 12 weeks of increasingly challenging cycling appeared to boost glymphatic flow and was related to changes in immune- and inflammation-related protein biomarkers. The findings suggest that improved glymphatic flow may be a potential mechanism underlying the protective effects of exercise on brain health, but more evidence is needed to prove it actually boosts waste removal or protects cognition.

Other suggestions of how to “detox your brain” circulating on social media have less support. Claims that changing the position you sleep in, for instance, originate from a 2015 study, which showed that rodents that slept on their right-hand side had more efficient glymphatic flow and increased clearance of beta-amyloid than rodents that slept on their back or front. Tantalising indeed, but unfortunately, no follow-up trials have been carried out in humans.

Likewise, there are claims that yogic breathing – which involves intentional, controlled and sometimes modified breathing techniques such as holding one nostril – can help brain clearance. While small studies suggest that this boosts the movement of cerebrospinal fluid around the brain, potentially helping with nocturnal housekeeping, there’s no evidence of it affecting the glymphatic system or waste removal just yet.

The one thing we should probably all focus on is getting a good night’s sleep. Here the evidence is clearer: deep sleep is associated with more efficient glymphatic clearance in animals, while evidence shows that people with sleep disorders tend to have impaired glymphatic function. Together, it gives another reason to try to improve your sleep habits, even if we can’t prescribe a precise sleep routine that optimises brain clearance.

How to tell if our brain detox is working

One of the major hurdles of all of this is that it is really hard to measure glymphatic flow in humans. Current methods are slow, invasive and expensive. Iliff wants tools that are non-invasive and easily used in clinics, “whether that’s a better MRI sequence, whether that’s [multiple] biomarkers, whether that’s the output of a wearable device”.

He works with a company called Applied Cognition, which has developed a wearable device that applies a gentle alternating electrical current to the brain and measures how well it passes through different regions. This seems to capture increases and decreases in glymphatic flow, which change how readily electricity can pass through. “That looks very promising,” he says. The device is still awaiting approval by the US Food and Drug Administration.

Another simpler, albeit indirect, measure of glymphatic efficiency could come from something you might already own – a smartwatch. A study published in August, which Nedergaard worked on, found that tiny fluctuations in heart rate vary in line with the noradrenaline oscillations driving glymphatic pumping. This suggests that heart rate variability – a metric recorded by most smartwatches – might offer a window into the brain’s waste clearance, potentially allowing people to monitor it at home and see whether changes in their habits make a difference. Bill agrees that this makes physiological sense, but she wants to see it tested directly.

Ultimately, better measurements in humans would allow researchers to establish which interventions boost clearance, before tackling the bigger question of whether that improves cognition and prevents disease.

It perhaps isn’t yet the revolution many hoped for. However, with so many interventions being trialled, hope is still high that some will prove successful. “It’s something that a lot of people are working on,” says Hauglund.

“Glymphatic function has entered the therapeutic era,” says Iliff. “The gates are open for evaluating therapeutics and evaluating interventions that modulate glymphatic function in people.” The challenge now is to figure out which ones make a meaningful difference.