Allergens: Chemical Sensitivity

What is IEI?

Idiopathic environmental intolerance (IEI) is a set of symptoms caused by contact with some kinds of substances. It used to be known as multiple chemical sensitivity (MCS). People with IEI have symptoms when exposed to low levels of common substances. Symptoms can include fast heart rate, sweating, and feeling dizzy.

What causes IEI?

Researchers are doing studies to learn the causes of IEI. It is not an allergic reaction. It does not cause the release of chemicals by the immune system. The physical cause is hard to find. Because of this, some studies suggest IEI may be linked to psychiatric disorders. These include somatoform disorders, depression, and anxiety. IEI occurs more in women than in men. IEI happens more often in people in their 30s or 40s.


Substances that cause symptoms are called triggers. These may be synthetic or natural substances. Triggers can include:

  • Caffeine

  • Food additives

  • Carpet and furniture

  • Plastics

  • Perfumes and other scented products

  • Paint

  • Cigarette smoke

  • Smoke from wood-burning stoves

  • Inhaled ozone and nitrogen dioxide

  • Inhaled sulfur dioxide

  • Dust storms, forest fires, volcano ash

  • Vehicle exhaust, petroleum refining, fossil fuel combustion

  • Cleaning fluids

  • Pesticides and herbicides


People with IEI may have symptoms such as:

  • Increased heart rate

  • Chest pain

  • Sweating

  • Shortness of breath

  • Fatigue

  • Dizziness

  • Warmth and redness of the face and neck (flushing)


Treatment for IEI may include:

  • Staying away from triggers

  • Counseling that may include cognitive-behavioral therapy (CBT)

  • Medicines for some symptoms

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