Key takeaways:
An electroencephalogram (EEG) is a painless test that measures your brain’s electrical activity.
EEGs can help diagnose seizures and other brain conditions.
You may need EEG monitoring for only a brief period of time or for several hours. It can take several days to get your EEG results.
An electroencephalogram (EEG) is a painless test that measures brain activity. Since its invention 100 years ago, EEGs have been used to help diagnose seizures and other brain conditions. If you or a loved one needs an EEG, here’s everything you can expect from this test, including tips to prepare.
What conditions does an electroencephalogram (EEG) diagnose?
EEGs help diagnose seizure disorders. Your healthcare team may recommend an EEG if you have new seizures or if you have a seizure disorder and are having more seizures than usual.
They’re also helpful when it’s not clear if a person is having seizures. For example, people who are nonverbal and have limited mobility from conditions like cerebral palsy may have subtle or no physical activity when they have seizures.
EEGs can also help diagnose:
Infections like meningitis and encephalitis
Brain illnesses like encephalopathy
Brain death
People with certain types of brain tumors or those who need brain surgery often need to get an EEG.
How does an EEG work?
An EEG measures the brain’s electrical activity. It’s similar to an electrocardiogram (EKG), except that an EKG measures the electrical activity of your heart instead of your brain. An EEG setup includes:
Electrodes
Wires
A monitor
A camera
During an EEG, a specialist places electrodes on parts of your scalp that correspond to different parts of the brain. These electrodes attach to wires. And the wires connect to a computer. The computer displays the electrical activity the electrodes pick up. The computer also records the electrical activity so that a physician can review in real time or later on.
Supporting someone with seizure disorder: It’s important to stay calm when a loved one is in crisis, as this brother learned when his teenage sister had her first seizure.
Knowing which meds can cause seizures: Certain medications could make you more likely to have a seizure by lowering your seizure threshold.
Taking lamotrigine for seizures: This medication treats certain types of seizures but may come with side effects. Learn about 11 lamotrigine side effects and how to manage them.
There might also be a video camera attached to the computer to provide a live feed. The video also records for later review.
What are the different types of EEGs?
There are different types of EEGs, but they all work the same way. The difference is in their setup:
Standard EEG: A standard EEG lasts about 1 hour. You may be asked to do certain activities, like breathing fast or looking at flashing lights.
Continuous EEG: This is the same as a standard EEG but lasts longer. These are used in hospitals and may include a video camera.
Sleep EEG: Sleep EEGs can be helpful if you’re having seizures during sleep. You may need to wear the EEG monitor overnight. This can take place in your home or at a medical facility.
Video EEG: These include a video camera and may be short (a few hours) or long (over 8 hours). You’ll wear the EEG monitor and have a video camera facing you. If the EEG is picking up unusual brain activity, your healthcare team can watch the video to see what you’re doing when that activity happens. These types of EEGs happen at a medical facility.
Ambulatory EEG: Similar to the video EEG, this type of EEG captures seizures during daily life. You’ll wear a cap with electrodes that attach to a portable cassette recorder. You can go about your daily routine, and the EEG will pick up your brain activity.
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How long does an EEG take?
EEGs can be short or long, depending on the type of EEG. A standard EEG lasts about 1 to 2 hours. A typical sleep EEG lasts at least 3 to 4 hours. Video, ambulatory, and continuous EEGs last anywhere from 8 to 24 hours — and sometimes longer.
Remember, the EEG is monitoring your brain activity in real time. If you don’t have unusual brain activity while wearing the EEG, then the test might not be helpful. That’s why you may need a longer EEG. You may also need repeat EEGs to increase the chances of capturing unusual brain activity.
Risks of an EEG test
An EEG is a painless and noninvasive test. So it carries fewer risks than other types of medical procedures. Some risks of EEG include:
Seizures: You may be asked to do things during an EEG that can provoke a seizure like breathing fast or looking at flashing lights. This can help capture your brain activity, but seizures can come with health risks.
Burns: EEGs can cause electrical burns if the machine isn’t properly set up. This is extremely rare.
How to get ready for an EEG
EEGs aren’t invasive or painful. So getting ready for one is relatively straightforward. Your healthcare team will go over specific instructions with you. Here are some general steps to expect:
You may need to stop taking your anti-seizure medications before the EEG. Always follow directions on how to safely stop these medications.
Don’t drink any caffeinated beverages for 8 to 12 hours before your EEG. Caffeine is a stimulant that affects your brain. It can interfere with the EEG results. You may also need to stop other stimulants, like ADHD medications.
Wash your hair with shampoo the night before or the morning of your EEG. Don’t apply any conditioner or other hair products. These products keep the electrodes from sticking to your scalp.
What happens after an electroencephalogram?
When your EEG is over, the technician will help you remove the electrodes and glue. A healthcare professional will give you the results over the phone or at a follow-up visit. It may take a few days to get your full results. The next steps will depend on your EEG results.
You can drive after an EEG. But you should arrange a ride home if you’re having a sleep-deprived EEG. You may feel groggy after and need help getting home.
Getting your EEG results
Your healthcare team will update you on your EEG results. You may get initial results as soon as you finish your EEG. But it can take several days for your team to review the entire test, especially if you had an EEG that lasted several hours or days.
EEGs are sometimes interpreted remotely by healthcare professionals that live in other areas. This allows people to get an EEG closer to home. But it also means that it can take a few days to get your results back and that you may not receive initial results right away.
Frequently asked questions
An EEG can’t tell if you had a seizure in the past. An EEG can only record your brain activity in real time.
Slowed brain activity is a sign of a medical condition that affects the brain. An EEG can capture slowed brain activity (slow brain waves). There are different patterns of slowed activity that indicate different types of medical conditions. You may need additional tests to pinpoint the cause of unusual brain activity noted on an EEG.
Collodion remover is great for removing EEG glue, but it’s not available over the counter. You can ask for some extra remover after your EEG. Consider bringing an empty travel bottle with you to fill at the medical office.
If that’s not an option, you can use skin-safe oil to remove glue. Massage the oil into any areas of your scalp where you still feel some glue. Let the oil sit for 10 to 20 minutes and then wash your hair with shampoo. The remaining glue will be loose enough to comb out. If you can’t get everything out, resist the urge to wash with hot water or pull the glue out. Both will damage your hair and scalp. Instead, keep applying oil and washing it out each day.
An EEG can’t tell if you had a seizure in the past. An EEG can only record your brain activity in real time.
Slowed brain activity is a sign of a medical condition that affects the brain. An EEG can capture slowed brain activity (slow brain waves). There are different patterns of slowed activity that indicate different types of medical conditions. You may need additional tests to pinpoint the cause of unusual brain activity noted on an EEG.
Collodion remover is great for removing EEG glue, but it’s not available over the counter. You can ask for some extra remover after your EEG. Consider bringing an empty travel bottle with you to fill at the medical office.
If that’s not an option, you can use skin-safe oil to remove glue. Massage the oil into any areas of your scalp where you still feel some glue. Let the oil sit for 10 to 20 minutes and then wash your hair with shampoo. The remaining glue will be loose enough to comb out. If you can’t get everything out, resist the urge to wash with hot water or pull the glue out. Both will damage your hair and scalp. Instead, keep applying oil and washing it out each day.
The bottom line
An electroencephalogram (EEG) is a painless test. An EEG monitors brain activity and helps diagnose seizures and other brain conditions. During an EEG, a specialist places electrodes on your scalp and a computer records your brain activity. EEGs can last anywhere from 1 to 24 hours, depending on the kind of EEG you need.
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References
Beniczky, S., et al. (2020). Electroencephalography: Basic biophysical and technological aspects important for clinical applications. Epileptic Disorders.
Britton, J. W., et al. (2016). An orderly approach to EEG analysis: Visual inspection of the background and pattern recognition. Electroencephalography (EEG): An Introductory Text and Atlas of Normal and Abnormal Findings in Adults, Children, and Infants. American Epilepsy Society.
Britton, J. W., et al. (2016). Appendix 3. Principles of electrical safety. Electroencephalography (EEG): An Introductory Text and Atlas of Normal and Abnormal Findings in Adults, Children, and Infants. American Epilepsy Society.
Britton, J. W., et al. (2016). Appendix 6. A brief history of EEG. Electroencephalography (EEG): An Introductory Text and Atlas of Normal and Abnormal Findings in Adults, Children, and Infants. American Epilepsy Society.
Britton, J. W., et al. (2016). The abnormal EEG. Electroencephalography (EEG): An Introductory Text and Atlas of Normal and Abnormal Findings in Adults, Children, and Infants. American Epilepsy Society.
Debicki, D. B. (2017). Electroencephalography after a single unprovoked seizure. Seizure.
Emmandy, P. D., et al. (2025). EEG abnormal waveforms. StatPearls.
Epsy. (2025). How to get EEG glue out of hair.
