Carbon Monoxide Poisoning — Symptoms and Treatment

Carbon monoxide (CO) is produced by incomplete combustion — any device that burns fuel (gas, oil, wood, charcoal, petrol) can produce it under certain conditions. It is colourless, odourless, and tasteless. A person exposed to CO has no sensory warning. The only reliable early warning is a functioning CO detector.

CO binds to haemoglobin — the protein in red blood cells that carries oxygen — with approximately 250 times the affinity of oxygen. This means CO molecules displace oxygen and are not released as quickly, progressively depriving body tissues of oxygen even while the person continues to breathe. The brain and heart, which have the highest oxygen demands, are affected first and most severely.

How CO Affects the Body

Blood CO Level (COHb%)	Effect
< 10%	No symptoms in most people; mild effects in sensitive individuals
10–20%	Headache, fatigue, shortness of breath on exertion
20–30%	Moderate headache, throbbing, nausea, dizziness, impaired judgement
30–40%	Severe headache, vomiting, drowsiness, confusion
40–50%	Extreme confusion, rapid heartbeat, collapse possible
50–60%	Seizures, loss of consciousness
> 60%	Coma, cardiac arrest, death

The rate at which CO levels rise depends on the concentration in the air and the duration of exposure. A high-concentration CO leak (e.g. from a faulty boiler or blocked flue) can take someone from apparently normal to unconscious in under an hour. A lower-level chronic leak may cause headaches and nausea for days before someone realises the cause.

Symptoms — What to Look For

Mild to Moderate Exposure

• Headache — the most common early symptom; often described as dull, throbbing, frontal
• Fatigue and lethargy — disproportionate tiredness
• Nausea — sometimes with vomiting
• Dizziness — especially when standing or on exertion
• Shortness of breath — particularly on exertion
• Difficulty concentrating — cognitive impairment, confusion

How to Distinguish CO Poisoning from Other Illness

CO poisoning is frequently mistaken for:

• Flu (without fever — CO does not cause fever)
• Food poisoning
• Migraine
• Winter virus

Key distinguishing features:

Feature	CO Poisoning	Flu / Virus
Fever	No	Yes
Symptoms improve when leaving home	Yes	No
Multiple people / pets affected simultaneously	Often	Unlikely (flu spreads over days)
Pets unwell or dead	Possible	No
CO alarm activated	Yes	No
Symptoms worse at night or morning	Possibly (sleeping near source)	Variable

⚠️ The pattern of symptoms improving when away from home and worsening when at home is a key indicator of CO exposure. If you and another household member both have headaches and nausea, and you have gas appliances, get out and call the gas emergency number — do not assume it is a coincidence.

Severe Exposure

• Loss of muscle control
• Extreme confusion or disorientation
• Seizures
• Loss of consciousness
• Breathing difficulties (may appear to stop)
• Skin and mucous membranes may appear pink or cherry red (not reliable; can also appear normal)

What to Do — Immediate Response

If you suspect CO poisoning — whether from symptoms, a triggered alarm, or both:

1. Open doors and windows immediately as you move to exit.
2. Get everyone out of the building — including pets.
3. Do not go back in to collect belongings, check appliances, or help animals still inside unless you can do so in under 10 seconds.
4. Call 999 (UK) or 911 (US) once outside — state that you suspect carbon monoxide poisoning.
5. Do not re-enter the building until emergency services and gas engineers have confirmed it is safe.
6. Move anyone unconscious away from the source into fresh air — if outside is not possible, to the freshest available air.

First Aid for CO Poisoning

Conscious person:

1. Get them to fresh air immediately.
2. Sit them down and encourage calm, slow breathing.
3. Do not let them walk back toward the source — they may feel well enough but remain at risk.
4. Call 999 / emergency services regardless of how they feel — CO levels in the blood continue to affect the body for hours.
5. Keep them warm — CO poisoning can cause a drop in body temperature.

Unconscious person:

1. Get them to fresh air.
2. Check for breathing — if breathing, place in the recovery position.
3. If not breathing — start CPR immediately.
4. Call 999 immediately.

Do not give the person alcohol or caffeine. Do not let them sleep it off without medical attention.

Medical Treatment

At hospital, CO poisoning is treated with:

• High-flow oxygen via a tight-fitting mask — accelerates the displacement of CO from haemoglobin. The half-life of COHb is approximately 4–5 hours breathing room air; it drops to approximately 60–90 minutes with 100% oxygen.
• Hyperbaric oxygen therapy (HBO) — in severe cases, involves breathing 100% oxygen in a pressurised chamber. Accelerates CO clearance further and may prevent delayed neurological complications.

Seek emergency medical treatment for any case of suspected CO poisoning — even if the person feels recovered after fresh air, CO damage can have delayed neurological effects, particularly in children, the elderly, and pregnant women.

Long-Term Effects

Significant CO exposure can cause lasting effects:

• Neurological damage — memory problems, personality changes, difficulty concentrating
• Cardiac damage — CO affects the heart at high concentrations
• Pregnancy complications — CO crosses the placenta; foetal haemoglobin has higher CO affinity than adult haemoglobin
• Delayed neurological syndrome — symptoms that appear to resolve then recur weeks later

This is why medical evaluation after any CO exposure is important, even when the person appears recovered.

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Quick Reference

Situation	Action
CO alarm sounds	Evacuate immediately; call 999; do not re-enter
Headache + nausea that improves outside	Suspect CO; evacuate; call gas emergency
Multiple people unwell simultaneously	Suspect CO; evacuate; call 999
Person unconscious, CO suspected	Fresh air; CPR if not breathing; call 999
Person recovered after fresh air	Still seek medical attention; CO effects are delayed
CO detector activated, no symptoms	Still evacuate — you may not feel symptoms yet