As per the World Health Organization, all but 1% of the world's population is exposed to unhealthy air and also exceeds the WHO limits for pollutants. However, there are some parts of the world where aur quality has improved through policies that limits pollution, while in other parts, it has not reached the desired results.

For US, more than 25% of the population is exposed to "unhealthy" air as per the Environmental Protection Agency (EPA), this is according to the report by the climate non-profit First Street Foundation. By 2050, the number of people exposed to "unhealthy" air will increase by more than half. The worst days of air pollution, reports BBC, "hazardous" or maroon under the EPA's system will rise by 27%.

Why are we talking about this today? It is because of the recent wildfire in California, which started on January 7. This is also one of the factors that is spiking the PM2.5 levels. It has increased by up to five micrograms per cubic metre in the western US in the past decade.

What is PM2.5?

It is a type of air pollution which is made of particulate matter and measures 2.5 micrometres across or less. It is roughly 30 times smaller than the width of a human hair. These particles are made with a mixture of solid and liquid substances, which varies in their chemical composition, including carbon, metals, and organic compounds.

These specks of airborne soot, dust and other substances can also trigger inflammation, which could also damage your brain.

As per a 2021 study titled The Changing risk and burden of wildfire in the United States, a quarter of US's PM2.5 pollution was caused by wildfire smoke. In 2023, US also witnessed a significant dip in air quality and visibility as smoke from wildfires north of the Canadian border entered across the continent. In May 2024, Canada also saw a start to its wildfire season, and one town was evacuated in British Colombia.

Wildfire smoke and its effects

Wildfires do not only affect those who live near forests, peatlands, and grasslands, but also to the cities and environment in general. It can send plumes up to 14 miles or 23km into the stratosphere, and from there, it can spread all over the globe. For instance, in 2023, the Siberian wildfires released smoke that travelled across the Pacific Oceans to reach Alaska and Seattle.

Other than PM2.5, wildfire smoke is also harmful to immune cells in lungs, and the toxicity could be four times greater than particulates from other types of pollution.

Another 2019 study titled Effects of Atmosphere Processing on the Oxidative Potential of Biomass Burning Organic Aerosols found the toxicity of smoke doubled in the hours after it was first emitted and reached four times greater toxicity at its peak.

Health Impact

There have been research that shows how pollution affects your brain. It can lead to impaired judgment, poorer performance in school and even higher levels of crime, as per the 2018 study by the London School of Economics.

Other health concerns include weight gain. There have been researches that links airborne pollution such as PM2.5 to obesity. The studies have found that children who live in most polluted areas are twice as more likely to have obesity. Some studies also find the link of air pollution harming our sense of smell. As per an Italian study from 2022, titled Association between environmental air pollution and olfactory functioning among Italian adolescents and young adults in Northern Italy, noses of teenagers and young adults became less sensitive to odors after being exposed to nitrogen dioxide, which is a component in traffic fumes.

Delhi residents continue to struggle with deteriorating air quality, which is taking a visible toll on overall health. The Air Quality Index (AQI) across Delhi NCR crossed 400 on December 15, 2025, placing it firmly in the ‘hazardous’ category. With breathing outdoor air becoming increasingly difficult, many people are turning to air purifiers for relief, both at home and in offices. Yet a common concern persists. Are air purifiers truly safe, or do they come with hidden drawbacks? And can excessive use cause problems of its own? We got in touch with Dr Aditya Nag, Assistant Professor, Department of Respiratory Medicine, NIIMS Medical College and Hospital, to know more about the same.

What Is An Air Purifier?

An air purifier, often referred to as an air filtration system, is designed to clean indoor air by filtering out harmful particles and pollutants. It works by pulling in air from the room, passing it through layers of filters, and releasing cleaner air back into the space. These devices are widely used in homes and offices to create a healthier and more breathable environment.

Dr Aditya Nag said, “Air purifiers are particularly helpful in removing dust, pollen, pet hair, mould spores, and other microscopic particles that can trigger allergies or worsen respiratory conditions. Their internal filters trap these pollutants, helping improve indoor air quality. In simple terms, they aim to make the air inside cleaner, safer, and easier to breathe.”

Are Air Purifiers Safe To Use?

Air purifiers rely on fans to draw air through one or more filters that capture pollutants before circulating cleaner air back into the room. They come in many forms, from portable units that can be shifted between rooms to wall-mounted models. There are also compact desktop versions and even wearable purifiers available today.

According to our health expert, air purifiers are generally safe and effective at improving indoor air quality, provided the right type is chosen and maintained properly. Models that use True HEPA filters and do not produce ozone are considered the safest. However, ozone-generating purifiers, certain UV-C devices without adequate shielding, and units with poorly maintained filters can release harmful by-products. These secondary pollutants may irritate the lungs and airways. This is why it is important to check safety certifications, replace filters on time, and avoid technologies known to emit ozone.

Overusing Air Purifiers Is Bad For Lungs?

Our expert points out that running an air purifier nonstop on high settings in tightly sealed rooms can reduce indoor humidity levels significantly. This drop in moisture can be uncomfortable for the respiratory system. “While clean air is important, the lungs function best when the air also has enough moisture,” he explains.

Very dry indoor air can irritate the nose, throat, and airways, leading to symptoms such as dryness, scratchy throat, persistent dry cough, burning eyes, and even frequent nosebleeds, especially in the morning.

Dr Nag stresses that air purifiers remain extremely useful, particularly for children, older adults, and people with asthma or allergies. The key is balanced use. He advises switching to auto mode instead of running turbo mode all the time, avoiding completely sealed rooms, and maintaining indoor humidity between 40 and 60 percent. This can be done with a humidifier or simple home measures.

Is It Safe to Sleep Near an Air Purifier?

Many people place air purifiers in their bedrooms, often close to the bed, which raises questions about safety during sleep. According to our expert, sleeping near an air purifier is generally safe and can even be beneficial, as long as basic precautions are followed.

Most modern air purifiers, especially those equipped with HEPA filters, are built for continuous use and operate quietly enough for bedrooms. By reducing allergens and airborne particles overnight, they may help improve sleep quality, particularly for people with allergies or breathing issues.

What To Look For In An Air Purifier?

When choosing an air purifier, it is important to look for models with True HEPA (H13 or H14) filters and activated carbon layers for effective removal of particles and odours. Check whether the purifier is suitable for your room size by reviewing its CADR, or Clean Air Delivery Rate. Noise levels are another key factor, especially if the device will be used in a bedroom.

It is also wise to consider the cost and frequency of filter replacement. Be cautious of purifiers that rely on ozone-producing ionisers or certain UV features. A reliable air purifier should offer multi-stage filtration, cover the intended space efficiently, and operate quietly without compromising safety.

For decades, mental health issues were explained as a result of many small genetic risks piling up over time. However, a study led by German scientists has now identified one gene whose specific variants could appear to directly impact psychiatric symptoms, even in the absence of neurological problems. In rare cases, the study suggests, a single faulty gene may be enough to directly cause mental disorders, much earlier tan doctors typically expect.

Scientists studying mutations in the GRIN2A gene found evidence that certain rare variants do not increase the likelihood of mental illness, but they appear to trigger it. This happens due to a clear biological mechanism, often in the beginning of childhood itself. The findings challenge long-held assumptions about how conditions like schizophrenia, anxiety, and mood disorders develop.

The findings are published in journal Molecular Psychiatry. The study describes GRIN2A null variants as the first known example of a single gene directly causing early-onset and even isolated psychiatric disorders, including early-onset schizophrenia.

How An Unexpected Pattern Emerged

The research team, led by Johannes Lemke from the University of Leipzig Medical Center, did not set out to study psychiatric genetics. They were working with a global registry of people diagnosed with GRIN2A-related disorders, most of whom were tested as children for epilepsy or developmental delays.

When the researchers began asking physicians about mental health diagnoses, a striking pattern emerged. Out of 121 individuals with disease-causing GRIN2A mutations, 25 had been diagnosed with psychiatric disorders. Of those 25, 23 carried null variants that completely shut down the gene’s function. In contrast, only 2 of 37 people with missense variants, which alter but do not eliminate the protein, developed mental illness.

To understand how high and unusual this risk was, the team of researchers compared their findings with 21 years of national health records in Finland. This included records of over 5 million people, and the results were stark.

The analysis of this large population showed that by age 12, carriers of GRIN2A null variants showed an 87-fold higher rate of psychotic disorder compared to the general population. Although this estimate was based on just four cases, risks for mood disorders were nearly 12 times higher, and anxiety disorder six times higher.

What stood out most was timing. Schizophrenia typically appears in late adolescence or early adulthood. Anxiety and mood disorders usually emerge in the teenage years or later. In people with GRIN2A null variants, symptoms began as early as ages 8, 10, or 12.

How Does This Gene Operate In Your Brain?

GRIN2A carriers instruction for making a protein known as GluN2A. This is a critical component of NDMA receptors, which help brain cells respond to glutamate, brain's main excitatory chemical messenger.

When GluN2A is missing, these receptors cannot assemble or function normally. This is what leads to disruption in brain signaling that appears to directly drive psychiatric symptoms. Unlike polygenic risk scores that reflect tiny contributions from thousands of genes, GRIN2A null variants remove a key part of the brain's signaling machinery in one decisive step.

Interestingly, people with missense mutations had similar rates of epilepsy and intellectual disability as those with null variants. But when it came to psychiatric illness, only null variants carried substantial risk.

Mental Illness That Comes Without Warning Signs

Six people in the study developed psychiatric disorders without any intellectual disability. Two of them never experienced epilepsy. Without any known family history, these individuals would have never undergone a genetic testing otherwise. Current psychiatric guidelines also do not recommend genetic screening for isolated mental illness. This is because most participants who were initially tested for seizures or developmental delays, cases with only psychiatric symptoms are likely undercounted. The true prevalence may be higher.

A Targeted Treatment Shows Early Promise

Four people with GRIN2A null-related psychiatric disorders were treated with the amino acid L-serine for over a year, at doses up to 500 mg per kilogram daily. All four showed improvement. In one case, hallucinations stopped entirely. Others saw paranoid symptoms resolve, behavioral control improve, or seizures decrease.

L-serine converts to D-serine in the brain, which helps activate NMDA receptors. Boosting this pathway may compensate for the missing GluN2A subunits, offering a targeted approach rather than trial-and-error treatment.

Rethinking Early Diagnosis

More than 80 percent of people with GRIN2A null-related mental illness also had epilepsy at some point, though seizures did not predict who developed psychiatric symptoms. In most cases, mental illness appeared after epilepsy had resolved.

The findings suggest genetic testing could eventually become part of evaluating early-onset psychiatric disorders. For a small but significant group of patients, the cause of mental illness may be clearly identifiable, biologically grounded, and potentially treatable.

For most people living with mental disorders, the origins will remain complex. But this research shows that, sometimes, the answer may lie in a single gene.

Four-year-old Sienna Dunion had initially flu-like symptoms, however her condition rapidly worsened, leading to a coma. What seemed like a simple flu was actually Acute Necrotising Encephalitis (ANE), a rare and severe brain disorder. After undergoing multiple surgeries and having removed 60% of her intestines, she is now struggling to walk and talk like from before.

How Did It Begin?

The first indication, which was very easy to miss was when she asked to return home five minutes after heading out to play with her scooter, reports The Independent. She had always been happy and exciting, so for her to return home so soon was not normal. She had also complained about feeling "cold and chilly" to her older sister, however, all of such symptoms were just seen as a common cold or flu signs.

As a result, her parents, Gary and Angelina Dunion, decided to keep her off school on Monday 17 November. Her temperature raised, no one was really concerned. All of these were cold and flu symptoms. She was still playing with her Barbies.

But it was on a Wednesday morning when she became unresponsive and had to make an emergency trip to A&E in Kettering. This is when she was induced into coma and diagnosed with the rare brain disease ANE.

Three weeks later, her family is facing the challenges to cope with the new changes which may take away how her daughter was before. Now, she requires years of intense rehabilitation to learn how to walk and talk again.

What is Acute Necrotising Encephalitis (ANE)?

Acute necrotizing encephalopathy (ANE) is a rare and serious brain condition that can cause sudden and rapid neurological decline after a viral infection, most often the flu or COVID-19. Because only a small number of cases have been reported worldwide, there is no standard treatment, making diagnosis and management especially difficult.

Sienna's father told The Independent, "For us, it’s really important that people can understand this has happened to a really healthy four-year-old girl who had no underlying issues. It has completely changed our lives overnight. What started as a flu has turned into a complicated brain disease and the last three weeks have just been horrendous.”

A Rare Diagnosis, But Urgent Care

Sienna had been feeling unwell on Monday and Tuesday, but it was on November 19 that her condition suddenly worsened. Her mother, Mrs Dunion, became alarmed when she tried to wake her and realised Sienna was unresponsive.

At A&E, doctors initially believed she was dehydrated after she tested positive for influenza. However, a CT scan showed unusual findings, including white lesions, while other test results remained unclear.

By 11 pm, doctors decided Sienna needed to be moved to the intensive care unit at Nottingham’s Queen’s Medical Centre. An MRI scan later confirmed a diagnosis of acute necrotising encephalopathy (ANE), a rare condition linked to viral infections.

Because of how uncommon the disease is, doctors designed a personalised treatment plan for her. This included plasma exchange, a procedure her family described as effectively washing her brain.

On Saturday, November 22, an ultrasound revealed a large build-up of fluid in her stomach. Sienna had to undergo emergency surgery, during which 60 per cent of her intestines were removed. Her father called it the hardest night of his life.

She later needed two more surgeries after air was found in her abdomen. Sienna now has a stoma bag and will live with short bowel syndrome for the rest of her life.

“The one thing doctors have been clear about is that she will not be the same when she fully wakes up,” Mr Dunion said. “She will need extensive rehabilitation.”

Although Sienna is awake, her father explained that she does not understand what is happening around her. She is weak, struggles to track with her eyes, and cannot eat on her own. The family is now fundraising to support her rehabilitation, including physiotherapy, speech and language therapy, feeding support, and changes needed at home.

A family struggling to cope

The couple also have a seven-year-old daughter, who is very close to Sienna. “They are best friends,” Mr Dunion said. “She keeps asking, ‘Where is Sienna? When can we be a family again?’”

He added that it is impossible to explain the seriousness of the situation to her. “I can’t tell her that she won’t be able to talk to her sister for a long time.”

“She was the most caring, easygoing four-year-old I’ve ever known,” her father said. “Even when she had a fever, she would check our temperature to make sure we were okay.”

He described her as a social child who loved being around other kids and had an infectious belly laugh. “We just don’t know if we’ll hear that laugh again,” he said.