Some people react to chemicals in their environments. These allergy-like reactions seem to result from exposure to a wide variety of synthetic and natural substances. Such substances can include those found in:

  • Paints
  • Carpeting
  • Plastics
  • Perfumes
  • Cigarette smoke
  • Plants


Source: National Institute of Allergy and Infectious Diseases

Multiple Chemical Sensitivity (MCS) Syndrome



Source: Ohio State University - Multiple Chemical Sensitivity - CDFS-192-96

What is MCS?

In theory, MCS is an adverse physical reaction to low levels of many common chemicals. Chemical sensitivity is generally accepted as a reaction by certain individuals to chemicals but debate rages on whether MCS is classifiable as an illness. One of the difficulties in classifying MCS as an illness has been the complex nature of chemicals in the environment and the interaction effects with and within the human body. The length of exposure, the concentration of the chemical(s), and the individual's threshold of resistance are also factors complicating a simple definition. In the relatively few but growing documented cases of severe reactions to chemicals, there seems to be no single stimuli or predictor of reactions. The most severe cases, often called either Environmental Illness or 20th Century Disease, sometimes result in individuals isolating themselves from society, synthetic products, and any type of chemical product.

What makes MCS so hard to identify?

Few products in our society do not include some synthetic or natural chemicals. While most people are generally unaffected by them, many of us have experienced some type of reaction, stimulated by synthetic chemicals at some time in a particular situation. Headaches, dizziness, and shortness of breath are sometimes symptoms of reactions to chemicals. These same symptoms, however, are also common to many other illnesses, diseases, stress, and stimuli. A related illness caused by environmental stimuli is that of Sick Building Syndrome. This condition has, over the last twenty years, gained credibility in scientific circles and there are well-documented cases of large percentages of building inhabitants or workers reacting to chemicals in the closed environment of the building.

Exposure to specific chemicals or any combination of chemicals has an impact on the human body. The interaction may be positive, negative, or neutral. Many synthetic chemicals imitate natural chemicals normally found in the human body, without many of which we would die. In great concentration, these same chemicals can be toxic. The variables of concentration and time are central to how the chemicals affect an individual. The amount of time exposed, the type of chemical, and the concentration of chemicals may contribute to the individual's reaction.

Various chemicals pass through the human body unless the level of chemical exceeds the body's ability to cleanse itself. Some chemicals may accumulate in the body, however; other chemicals have an additive effect in that the toxicity of one can add to the toxicity of another. Additivity and body burden are very different, but are not mutually exclusive. There are also chemicals that stimulate the breakdown of other chemicals. This is called an antagonistic effect. Antagonism is an outcome of the process; in the breakdown, a chemical might exacerbate the toxicity of another, or become more toxic in a synergistic relationship.

These interactions of chemicals can be isolated in laboratories, but the human body, and the unique ability of each body to respond to different chemicals in different ways, makes it difficult to understand the effects of any one chemical in a particular concentration on any person. Just as some people react to certain medications while others do not, the way one person reacts to a chemical in the environment may be entirely different than another person.