Multiple Chemical Sensitivity

  What You Need to Know About
  Carbon Monoxide and Multi-Sensory Sensitivity


    Carbon monoxide (CO) is the most common cause of toxic poisonings and deaths in America, and has been for over a century.  CO also may be the most common cause of MCS, but it causes a very specific type of MCS that we call Multi-Sensory Sensitivity or MUSES Syndrome.   MUSES Syndrome is caused only by CO poisoning and is characterized not just by hypersensitivity to chemicals but to all types of sensory stimuli, including light, sound, touch, hot or cold weather and even (in extreme cases) electromagnetic fields.    

    People who develop MCS after exposure to other toxins such as pesticides or mold may also be sensitive to one or two other types of sensory stimuli such as light and sound but what distinguishes the MUSES cases caused by CO poisoning is their sensitivity to EVERYTHING.   Click here to read about a typical case of MUSES syndrome published in First For Women magazine.

    Fortunately, MUSES syndrome is easily diagnosed; even years after exposure, it is marked by a deficiency in the body's ability to absorb oxygen from the blood which is easily tested and can be safely treated with the standard treatment for CO poisoning, which is supplemental oxygen.  More on treatment below.  

    How does CO cause multi-sensory sensitivity?  The public (and most doctors) are taught only that CO is an invisible, odorless and tasteless gas that can kill you in seconds at very  high levels of exposure.  But few know that CO at low levels is also vital for human life.  We and all other mammals produce CO constantly in the normal breakdown of our heme proteins  (such as hemoglobin in red blood cells, myoglobin in muscle, and cytochromes throughout the body) by an enzyme called heme oxygenase (HO).  

    This production of CO by HO is increased 10 to 100-fold in response to stress of any kind, whether physical, chemical, biological, or mental, which is why HO is known as the Universal Stress Enzyme.  CO also is produced by the breakdown of certain inhaled and ingested chemicals such as methylene chloride, aka dichloromethane, which is a common solvent and propellant used in spray cans of all kinds.  

    After people have been CO poisoned, they may become hypersensitive thereafter to even very low levels of CO exposure (just as ex-alcoholics and ex-addicts become hypersensitive to their drug only after they quit).  They actually become so sensitive to CO that they overreact to even the relaitvely low levels produced by their body in response to stress of any kind.  

    While some of the CO produced by the body is bound tightly to hemoglobin, transported to the lungs, and exhaled, most binds to other proteins and is active in at least 90 pathways, including as a gaseous neurotransmitter in the regulation of learning, memory, heart rate, respiration and vasodilation. Of most significance to people with MCS is that CO controls sensory sensitization and adaptation to odors, lights, sounds and all other types of sensory stimuli.  

    These effects occur at relatively low levels of CO (under 5 parts per million in non-smokers), so--unless adapted or habituated to much greater exposures (as smokers are, for example)--most humans are very sensitive to breathing or producing small amounts of CO.    For a more detailed explanation supported by dozens of medical references, see our 
background paper on Sources, Symptoms, Biomarkers and Treatment of Chronic Carbon Monoxide Poisoning.

CO poisoning should be suspected whenever any of the following "flu-like" symptoms persist or recur regularly indoors, especially if affecting more than one person (or pet) at a time:

  1. Headache
  2. Fatigue, Weakness
  3. Muscle Pain, Cramps
  4. Nausea, Vomiting
  5. Upset Stomach, Diarrhea
  6. Confusion, Memory Loss
  7. Dizziness, Incoordination
  8. Chest Pain, Rapid Heart Beat
  9. Difficult or Shallow Breathing
  10. Changes in Sense of Hearing, Vision, Smell, Taste and Touch
    (from more common multi-sensory sensitivity at one extreme to less common loss of smell, taste, hearing and/or vision at the other extreme)

The standard treatment for CO poisoning is 100% oxygen (humidified) via a tight fitting non-rebreather mask. Oxygen also can be taken without humidification if inhaled into the nose via a canulus (without a mask), which most people with multi-sensory sensitivity tolerate better than a mask.  Symptoms usually improve within weeks of daily oxygen therapy (2hours per day), although it usually takes 3 to 4 months of daily therapy until people can stop taking oxygen without their CO symptoms returning.  

    To see if you may may benefit from oxygen treatment, we recommend you print out MCS R&R's 2-page protocol  for diagnosis and treatment of CO poisoning and complete the questionnaire on page 1. Take this along with page 2 to any local physician you like who is willing to prescribe the recommended arterial and venous blood gas tests  to determine if you have low oxygen uptake and could benefit from oxygen therapy.   Although some physicians have the equipment needed to test blood gases in their office, most will need to send you to a hospital blood gas lab.  

Unfortunately people with pure MCS (and no multi-sensory sensitivity) do not usually have a problem with oxygen uptake and so cannot be cured by oxygen therapy.  But supplemental oxygen may help people with other disorders whose symptoms clearly overlap with and may be caused by CO poisoning:

Alzheimer's *  Asthma * Attention Deficit Disorder * Autism * Chronic Fatigue Syndrome * Depression * Dysautonomia * Fibromyalgia * Irritable Bowel Syndrome * Lupus (SLE) * Migraine * Neurally Mediated Hypotension * Panic Disorder * Parkinson's * Pre-Menstrual Syndrome * Reactive Airways Dysfunction Syndrome * Reflex Sympathetic Dystrophy * Stress (since all stressors increase CO production)

Since CO cannot be smelled, seen, tasted or felt, the only way to detect exposure is with a CO ALARM (which have digital displays only from 30ppm to 999ppm and alarms only above 70ppm, as specified by UL) or a low-level CO MONITOR (which has a digital display below 30ppm, as recommended by UL for pregnant women, children, the elderly and people with chronic health conditions that put them at greater risk).  Two types of low level CO monitors are available from, the CO Experts model for home use and the PocketCO for portable use. 

If you have any of CO sources listed below in your home, you should install a CO alarm or monitor near the bedrooms since most CO deaths occur at night while people are sleeping. You also may want to keep a portable CO monitor in your vehicle since CO levels can build up quickly inside cars and trucks while driving (and especially idling) in heavy traffic, the most common outdoor source of CO . The most common indoor sources of CO are combustion appliances (gas ranges and ovens, gas water heaters, gas space heaters, gas and oil furnaces, gas and wood fireplaces), vehicles and small engines started in attached garages (especially in winter, as gas engines produce more CO when cold), and smoke from tobacco products (cigarettes, pipes, cigars), candles and incense.

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Last Modified: 10/23/06