If you’ve been exposed to carbon monoxide, get into fresh air immediately and call 911. Even if your symptoms feel mild, carbon monoxide poisoning requires medical evaluation because the gas displaces oxygen in your blood and can cause damage that isn’t obvious right away. What you do in the first minutes matters, but so do the days and weeks that follow.
Get Out and Get Help
Leave the building immediately. Don’t stop to open windows or search for the source of the leak. Take everyone with you, including pets, and move to open air. Once you’re outside and safe, call 911.
The classic symptoms of carbon monoxide poisoning are headache, dizziness, nausea, shortness of breath, weakness, and confusion. But here’s the problem: these symptoms overlap with the flu, food poisoning, and dozens of other conditions. The key clue is usually context. If multiple people in the same building feel sick at the same time, or if symptoms improve when you leave and return when you go back inside, carbon monoxide is a strong possibility.
Do not re-enter the building until a professional has confirmed it’s safe. Carbon monoxide is colorless and odorless, so you cannot tell whether it has cleared on your own.
What Happens at the Hospital
At the emergency room, doctors will give you high-flow oxygen through a tight-fitting face mask. This is 100% pure oxygen, far more concentrated than room air, and it works by forcing carbon monoxide out of your red blood cells so they can carry oxygen again. Standard pulse oximeters can’t distinguish between oxygen and carbon monoxide attached to your blood cells, so a normal reading on a finger clip doesn’t rule out poisoning. The hospital uses a specialized blood test that directly measures how much carbon monoxide is bound to your hemoglobin.
A level of 10% or higher, combined with symptoms, generally confirms poisoning. Levels reaching 20 to 25% with symptoms suggest severe oxygen deprivation to the brain and heart. That said, the correlation between blood levels and how sick someone actually is can be weak. Someone with a lower reading can still have significant symptoms, especially if the exposure lasted a long time.
In severe cases, such as loss of consciousness, significant confusion, or heart-related symptoms, doctors may recommend hyperbaric oxygen therapy. This involves breathing pure oxygen inside a pressurized chamber, which drives carbon monoxide out of the blood much faster than a regular face mask. Not every hospital has a hyperbaric chamber, so this sometimes requires a transfer.
Watch for Delayed Neurological Problems
One of the most important things to understand about carbon monoxide poisoning is that you can feel better, go home, and then develop new symptoms days or weeks later. These delayed neurological effects can appear up to six weeks after the initial exposure, even in people who seemed to recover fully.
The symptoms of this delayed reaction look very different from the original poisoning. They include memory problems, difficulty concentrating, mood changes or emotional instability, seizures, movement disorders resembling Parkinson’s disease, difficulty speaking, and urinary incontinence. Not everyone who experiences carbon monoxide poisoning develops these complications, but they are well documented and can be serious.
The CDC recommends a follow-up medical and neurological exam two weeks after discharge. This checkup typically includes a cognitive assessment to screen for subtle changes in memory, attention, or reasoning that you might not notice on your own. If you or someone close to you notices personality changes, new forgetfulness, or difficulty with tasks that used to be easy, bring that up with your doctor promptly rather than waiting for a scheduled visit.
Pregnancy and Carbon Monoxide
Carbon monoxide is especially dangerous during pregnancy. The gas crosses the placenta and can build up to higher concentrations in the fetus than in the mother. The fetus also eliminates it far more slowly, with a half-life roughly four to five times longer than the mother’s. This means the baby is still being affected long after the mother feels fine.
Severe maternal poisoning involving loss of consciousness has been associated with fetal death, congenital malformations, and neurological problems in the baby. Even chronic low-level exposure during pregnancy has been linked to preterm delivery and low birth weight in some studies. Treatment for pregnant patients starts the same way as for anyone else: high-flow oxygen immediately. However, because the fetus clears carbon monoxide so much more slowly, treatment duration is typically extended to roughly five times what would be needed to bring the mother’s levels back to normal.
Making Your Home Safe Before Returning
Before anyone goes back inside, you need to identify and fix the source of the carbon monoxide. A qualified technician should inspect all fuel-burning appliances, which include gas and oil furnaces, gas water heaters, gas ranges and ovens, gas dryers, gas or kerosene space heaters, fireplaces, and wood stoves. The technician should also check that all flues and chimneys are properly connected, in good condition, and not blocked by debris or animal nests.
Common sources of carbon monoxide leaks include cracked heat exchangers in furnaces, blocked or disconnected vents, and appliances that were never designed for indoor use. Generators, charcoal grills, and camp stoves used inside a home or garage are a leading cause of carbon monoxide emergencies, particularly during power outages.
Once repairs are complete, install carbon monoxide detectors on every level of your home and near sleeping areas if you don’t already have them. The EPA recommends having fuel-burning appliances professionally inspected at the start of every heating season, not just after an incident. For reference, workplace safety standards set the safe limit for carbon monoxide at 25 to 50 parts per million over an eight-hour period, with 200 ppm considered the absolute ceiling for even brief exposure. Home detectors typically alarm at lower thresholds to protect children, older adults, and others who are more vulnerable.
Recovery After Mild to Moderate Exposure
Most people with mild poisoning recover fully once they’ve received oxygen therapy and the source of exposure is eliminated. Headaches and fatigue may linger for a few days. During this time, rest, stay well hydrated, and avoid strenuous activity that increases your body’s demand for oxygen.
For moderate to severe cases, recovery is less predictable. Some people experience persistent fatigue, trouble concentrating, or mood changes for weeks or months. If delayed neurological symptoms do develop, rehabilitation may involve cognitive therapy, physical therapy, or psychological support depending on which functions are affected. The two-week follow-up exam is your best early warning system. Don’t skip it, even if you feel completely back to normal, because some cognitive changes are subtle enough that you won’t catch them yourself.