592 Criteria” and they lay the foundation for much of general causation oversight in the courts today. There is much more medical knowledge about the cause of common allergic diseases than about causes of cancer. Consequently, when epidemiologic studies have not estab- lished chemical X to be a carcinogen, it is methodologically improper for an oncology expert to assert that it caused his patient’s cancer. For pure allergy matters, by contrast, clini- cians properly rely on medical evidence which is not always supported by epidemiological studies. The chemical nature of a substance, its potential as an allergen, and clinical experience in many patients is often sufficient. However, allergists also deal with non-allergic responses which pres- ent general causation conundrums requiring epidemiology and basic toxicology in order for a general causal assertion to be justified. Consider, for example, a claim of irritation associated or suspected with a workplace chemical, new furniture or carpet, fresh paint, or a perfume. Consider the progression of this irritation into Multiple Chemical Sensitivity Syn- drome, a medically unproven condition. Before the allergist asserts that the patient’s symptoms and/or clinical manifes- tations were caused by the irritant effects of the chemical alleged, he/she had better know that that chemical is, in fact, an irritant and at what levels such effects occur. This can generally be found in the basic toxicological literature [15–17]. So, while formaldehyde can be mildly irritating at between 0.1 and 0.3 parts per million, benzene, toluene, and most other common organic chemical constituents of paints, gasoline, and perfume are not [18, 19]. Alcohols, simple aliphatic hydrocarbons, and a simple benzene ring generally have mild-to-no irritating properties, whereas aldehydes and ketones are significantly more irritating. The allergist must assume that, if he asserts the existence of a causal link between symptoms and the alleged chemical irritant in the context of his patient’s claim, he will be questioned about basic toxicological principles pertaining to irritation and chemical structure. It is, after all, fair game for the opposing attorney to ask about and to challenge the methodology which led the physician to reach his general causal conclu- sion. And, in this case, that methodology is premised upon the basic toxicological/irritant properties of the relevant chemicals. Certain general causation questions of dubious estab- lished connection may confront the allergist. An example may be the multi-organ, multi-system complaints which the patient has attributed to mold or mold toxins. Everything from cognitive dysfunction to gastrointestinal disturbances fall into the category of common symptoms with little general causal scientific support [20–26]. The allergist who affirms the patient’s causal belief in such matters can expect probing questioning about the scientific merits of that claim by a well-prepared attorney. Curr Allergy Asthma Rep (2012) 12:590–598 Specific Causation Once the general causation question is asked and answered affirmatively, the physician can move on to the specific causation issue. Now that we have established the plausibil- ity of the contended causal relationship, we must answer the question: “Has it actually occurred in this patient?” Specific causation is made up of several essential sub- parts: (1) the dose must have been sufficient to have caused the claimed adverse health outcome; (2) the temporal rela- tionship must have been correct; (3) if the claimed disorder is allergenically-based, the individual must have demon- strated allergic sensitization to the agent(s) at issue; and (4) other causes must have been considered and ruled out. Figure 1 illustrates the distinction between the diagnostic methodology and the causation assessment methodology. An evaluation begins with a quest for the diagnosis utilizing a standard differential diagnostic approach. Causation as- sessment, a distinct and separate process, follows utilizing the principles previously delineated. The Role of Differential Diagnosis in Causal Analysis From a scientific/medical perspective, the law requires that the expert who is providing a medical opinion on causation follow a methodology consistent with the methodology utilized by his peer group. In the past few years, a growing number of courts have, quite improperly, in our opinion, taken that requirement to mean that the process of differen- tial diagnosis would properly lead to both a diagnosis and a causal conclusion. Figure 1 illustrates why that is not the case. If it were true that the diagnostic process uncovered an external cause with no further analysis required, a physician could ascribe any cause of his/her choosing to an ailment, whether or not there was even a modicum of scientific support for such a connection. He could simply assert that the patient suffers from a disorder of his own invention and that his conclusion was the result of having excluded all other conditions in the differential diagnosis. A causal con- clusion requires an analysis quite separate from a diagnosis. The fact that an oncologist establishes a diagnosis of acute myelogenous leukemia and states that it was due to benzene exposure does not mean that he/she has supported that causal attribution. Simply asserting that the patient has AML caused by benzene does not make that assertion correct. To be correct, the general and specific methodolog- ical approaches necessary for specific causation delineated above must have been followed. The same can be said for a diagnosis by an allergist. One might diagnose probable occupational asthma rather than exacerbation of non-occupational adult-onset asthma, but such a conclusion needs more that a history alone to