Environmental sensitivities are a range of reactions to environmental factors including chemicals, foods, biological agents and electromagnetic radiation, at levels of exposure tolerated by many people. It encompasses a range of overlapping chronic conditions such as Multiple Chemical Sensitivity (MCS) and Electromagnetic Sensitivity.

Environmental sensitivities frequently contribute to illnesses such as Chronic Fatigue Syndrome/Myalgic Encephalomyelitis (CFS/ME) and Fibromyalgia (FM).

In 1999, group of physicians and researchers published the criteria for diagnosis of MCS. Case Criteria - 1999 Consensus on Multiple Chemical Sensitivity (MCS)

• Symptoms are reproducible.
• The condition is chronic.
• Low levels of exposure (lower than previously or commonly tolerated) result in
symptoms.
• Symptoms improve or resolve when incitants are removed
• Responses occur to multiple chemically unrelated substances.
• Symptoms involve multiple organ Systems.