In Westberry v. Gislaved Gummi AB, 178 F.3d 257 (4th Cir. 1999), the plaintiff alleged severe sinus problems due to inhalation of talc. Id. at 260. The defendant argued that the physician's differential diagnosis expert testimony should have been ruled inadmissible as scientifically unreliable because the expert had no epidemiological or animal studies, no published peer-reviewed studies, or laboratory data to support talc as a causative agent for sinus disease. Id. at 262. However, the Fourth Circuit held that "differential diagnosis, or differential etiology, is a standard scientific technique." Id. at 262. The Court rejected defendant's challenge to plaintiff's expert medical testimony where accumulations of talc were evident in the environment although the level of airborne talc was never measured and plaintiff's tissue concentration of talc was never determined. Id. at 263-66. The court stated that it must be recognized that "only rarely are humans exposed to chemicals in a manner that permits a quantitative determination of adverse outcomes. . . . Human exposure occurs most frequently in occupational settings where workers are exposed to industrial chemicals like lead or asbestos; however, even under these circumstances, it is usually difficult, if not impossible, to quantify the amount of exposure." Id. at 264 The Court of appeals ruled that, with regard to whether a physician could testify about causation concerning whether exposure to talc could produce a sinus irritation, the absence of specific levels of talc exposure was not necessary as "there was evidence of a substantial exposure." Id. at 264.