What is multiple chemical sensitivity (MCS)?

What is multiple chemical sensitivity (MCS)?

Multiple chemical sensitivity (MCS) is a chronic medical condition characterized by strong physical reactions to low-level chemical exposure. Symptoms of MCS typically can include:

- Eye irritation and rhinitis

- Wheezing and fatigue

- Skin rash and sore throat or cough

The term “multiple chemical sensitivity” first came into use in the 1980s. Since then, there has been a debate over the scientific basis for MCS. The American Medical Association (AMA) does not recognize MCS as an official medical disorder. However, many individual doctors do. As many as 15% of the U.S. population suffers MCS symptoms. In Australia, nearly 25% of adults report sensitivity to chemical odours.

Research on MCS

The Karolinska Institutet in Stockholm, Sweden, used nuclear-imaging technology and other advanced techniques to identify the link between odors and MCS. Their research has defined at least two specific processes that cause those with MCS to react differently to odours.

Brain activity.

MCS patients process odours differently than the control group. Researchers used nuclear imaging to observe that MCS patients activate the odour-processing areas of their brains less frequently than the non-MCS individuals. Those with MCS also show an increase in activity in two other regions of the brain in response to odours.

Harm avoidance and serotonin.

MCS patients exhibit higher levels of harm avoidance, a measurable personality trait, than non-MCS patients. MCS patients also have reduced levels of 5-HT1A, a receptor in the nervous system that is activated by serotonin. Serotonin contributes to feelings of well-being and happiness. The researchers believe these deviations in the MCS sufferers’ physiology could make them intolerant to environmental odours.

What causes multiple chemical sensitivity?

A wide variety of chemicals and odours trigger MCS symptoms. Some of the most common include:

- Fragrances and hair-care products

- Nail polish and remover

- Tobacco smoke

- Insecticides

- Dry-cleaned clothing

- Alcohol

- Off-gassing of paint

- Some cleaning agents

- Gasoline

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