Head injury and air pollution

Two risks for dementia come from the world around us. One is a hard hit to the head. The other is dirty air. A major 2024 expert report listed both among 14 risk factors that people and communities may be able to change. Together, those 14 factors are linked to nearly half of dementia cases.¹

You cannot control every fall or every smoky day. But there is a lot you can do. This page explains what the research shows and the steps that matter most, especially for older adults.

What a head injury does to the brain

A traumatic brain injury is damage that changes how the brain works. It can happen from a bump, blow or jolt to the head. It can also happen when a hit to the body makes the head snap back and forth.³

A concussion is a mild TBI. Most brain injuries each year are mild.³ Even so, getting several concussions can slow recovery and may lead to lasting trouble with memory, focus, headaches or balance.³

Older adults are hit hardest. They are more likely than any other age group to be hospitalized or to die from a TBI.⁴ In 2021, more than 69,000 people in the U.S. died from TBI-related causes.⁴

How head injury is linked to dementia

Large reviews that combine many studies agree that a past TBI raises the chance of dementia. One review of 32 studies with more than 7.6 million people found the risk was about 1.7 times higher.¹

The size of the risk depends on how bad the injury was:

Not every study finds the same numbers.² Also, these are links, not proof that the injury alone caused the dementia. Other health problems can play a part.¹

Timing matters too. In one Swedish study, the chance of a dementia diagnosis was highest in the first year after a TBI. But some extra risk lasted as long as 30 years.²

There is no known treatment yet that lowers long-term dementia risk after a serious or repeated head injury.² That is why preventing the injury is so important.

Preventing falls: the biggest step for older adults

Falls cause nearly half of all hospital stays for TBI.⁴ More than 1 in 4 older people fall each year, yet fewer than half tell their doctor. One fall doubles the chance of another.⁶ Each year, older adults make about 4.5 million emergency room visits because of falls.⁶

The CDC recommends these steps:⁷

1. Talk with your doctor about falls. Ask for a fall risk check, even if you have not fallen.
2. Review all your medicines. Bring every pill bottle, including over-the-counter sleep aids and allergy pills, to your doctor or pharmacist. Ask which ones may cause dizziness or sleepiness. Do not stop any medicine on your own. See medicines that can worsen memory.
3. Ask about bone health. Ask whether you should be tested for osteoporosis (thin, weak bones), and whether vitamin D is right for you.
4. Build strength and balance. Exercises for your legs and balance lower fall risk. Tai chi is one good choice. Try our strength and balance routine or tai chi.
5. Check your eyes every year. Update your glasses. If you wear bifocals or progressive lenses, ask about a pair with only your distance prescription for walking outdoors. See hearing, vision and brain health.
6. Make your home safer. Clear things you could trip over. Put grab bars by the tub, shower and toilet. Add railings on both sides of stairs. Use more and brighter lights.

If you need a cane or walker, use it every time. Remove loose rugs and clutter.² Our pages on making the home safer and preventing falls give room-by-room checklists.

Helmets, seat belts and sports

A Cochrane review looked at bike helmets for people of all ages. Helmets lowered the risk of head, brain and severe brain injury by 63% to 88%. They protected riders whether or not a car was involved.⁸ These numbers come from well-run studies comparing injured riders, not from trials, but the results were strong and consistent.⁸ Moderate evidence

A helmet only works well if it fits. Sizes differ from brand to brand, so adjust the straps for your own helmet. A mirror or a friend can help.⁹

Other everyday steps:^1,2

• Wear a helmet for biking, skating, scooters and contact sports.
• Always wear a seat belt, follow traffic rules and keep your car in good repair.
• In youth and adult sports, limit heading the ball in soccer practice and high-impact collisions.
• Do not return to play right after a head injury. Let the brain heal first.

After a fall or hit to the head

Get medical care soon after a possible concussion. Early care can help recovery.³ In rare cases, a dangerous blood clot can form and press on the brain.⁵

A person living with dementia may not be able to explain a headache or new confusion. Caregivers should watch closely for changes for a few days after any fall. If the person takes a blood thinner, call the doctor after any bump to the head, even if they seem fine, and mention the medicine.

Air pollution and the brain

Air pollution includes tiny particles called PM2.5. They are far thinner than a human hair, so they can travel deep into the lungs. They come mostly from burning things, such as fuel in engines, wildfires, and wood or coal stoves.¹

The 2024 expert report pulled together 20 studies with more than 91 million people. For each small step up in long-term PM2.5 levels (1 microgram per cubic meter of air), dementia risk rose about 3%.¹ A stricter look at only five high-quality studies found a similar trend, but it was not certain enough to rule out chance.¹

Other findings from the report:¹

• Soot (black carbon, a part of PM2.5 from burning fuel) had the strongest link in one U.S. study of more than 18 million people.
• Gases such as nitrogen dioxide and ozone did not show a clear link.
• The effect seemed worst in people who already had heart disease.
• When pollution went down, dementia risk went down too, in studies from France and of older U.S. women.
• There may be no fully "safe" level. The World Health Organization's goal is a yearly average below 5 micrograms per cubic meter.

Indoor smoke counts too. Wood and coal stoves made up a large share of fine particle pollution in one country studied, and cooking or heating with solid fuel has been linked to higher dementia risk.¹ Tobacco smoke is another big source. See sleep, alcohol and smoking.

Much of air quality depends on laws and community action. The report calls on leaders to clean the air, especially where pollution is worst.¹ But you can still lower your own exposure.

How to breathe cleaner air

Check the Air Quality Index (AQI). It is a daily score from 0 to 500. You can find it at AirNow.gov, on many weather apps and in local news. Higher numbers mean dirtier air. Older adults are named as a group that is more sensitive to particle pollution.¹⁰

Source for the table: AirNow air quality guide for particle pollution.¹⁰

You can follow wildfires on AirNow's Fire and Smoke Map.¹¹ For a full plan for smoke, storms and power outages, see emergency and disaster planning.

Questions to ask your doctor

Am I at risk for falling?

• Can you check my balance, strength and walking?
• Do any of my medicines raise my risk of falling?
• Should I be tested for osteoporosis? Is vitamin D right for me?
• Would a physical therapist or balance class help me?

I had a head injury in the past. What should I know?

• Should my old injury change how you check my memory?
• What signs should I or my family watch for?
• How can I protect myself from another head injury?

Does air pollution affect my health conditions?

• I have heart or lung disease. At what AQI level should I stay inside?
• Is it safe for me to wear an N95 mask?
• What should I do on smoky days?

How this fits with other risk factors

Head injury and air pollution are only two of the 14 risk factors. The link between air pollution and dementia looks strongest in people with heart disease, so caring for your blood pressure and cholesterol matters even more.¹ Staying active builds the strength that prevents falls. For a simple daily plan that brings all of this together, see keeping your brain healthy, or return to the dementia guide.

Education only. This page is general information written from the sources listed. It is not medical, legal or financial advice and does not replace a doctor, therapist or lawyer who knows your situation. How we write and check pages.