MCS, or Multiple Chemical Sensitivity, is a condition where individuals experience adverse reactions to low levels of various chemicals in their environment. There are several synonyms for MCS such as environmental illness, chemical sensitivity, and toxicant-induced loss of tolerance. Other terms that can be used to refer to MCS include idiopathic environmental intolerance, sick building syndrome, and Gulf War Syndrome. These different terms reflect the various ways in which the condition can be triggered and the resulting symptoms. Regardless of the terminology used, it is important to understand that MCS is a serious health condition that can severely impact a person's quality of life.