Invited commentary: sensitivities to chemicals--context and implications.

The ground-breaking manuscript on chemical sensitivity symptoms by Kreutzer et al. (1) brings some long overdue rigor to the epidemiology of what has come to be called multiple chemical sensitivity (MCS). It also provides an opportunity to highlight work important to public health in an overlooked field, that of medically unexplained somatic symptoms. MCS along with other syndromes associated with unexplained somatic symptoms often receives relatively short scientific shrift. Symptoms (e.g., headache, fatigue, trouble concentrating) account for a high proportion of medical encounters, and a surprising majority are not explained by pathologic medical conditions (2, 3). Rather than simply dismiss these "unexplained symptoms," over at least the past two decades, practitioners and patients have coalesced these symptoms into syndromes including chronic fatigue syndrome (CFS), fibromyalgia (FM), irritable bowel syndrome (IBS), atypical connective tissue disease after silicone breast implants, chronic hypoglycemia, sick building syndrome (nonspecific building related illness), MCS, and, most recently, Gulf War Illness. Some of the names, such as CFS, do not imply etiology or pathophysiology, while others, such as MCS, invoke chemical triggering of symptomatic episodes as well as the often implied chemical initiation of the sensitivity. Investigators have pointed out the substantial overlap between one unexplained symptom classification and another, such that 30-50 percent of individuals with CFS, FM, and MCS qualify (based on self-report of symptoms) for at least one of the other diagnoses (4, 5). All are unexplained because, despite many theories and hypotheses, there is no acceptance by the medical community