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Idiopathic Environmental Intolerance (IEI)

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's not an allergic reaction. It does not cause the release of chemicals by the immune system. A 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 often 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. Reported triggers include:

  • Caffeine

  • Food additives

  • Carpet and furniture odors

  • Perfumes and scented products

  • Paint

  • Cigarette smoke

  • Vehicle exhaust, fuel odors

  • Pesticides and herbicides

  • Mobile telecommunication devices


People with IEI may have symptoms such as:

  • Increased heart rate, palpitations

  • Chest pain

  • Sweating

  • Shortness of breath

  • Fatigue

  • Dizziness

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

  • Nausea

  • Trouble concentrating

  • Cough

  • Numbness


Treatment for IEI may include:

  • Staying away from triggers

  • Counseling that may include cognitive behavioral therapy (CBT)

  • Medicines for some symptoms

Online Medical Reviewer: Deborah Pedersen MD
Online Medical Reviewer: Marianne Fraser MSN RN
Date Last Reviewed: 2/1/2024
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