NOT FOR PUBLICATION

UNITED STATES COURT OF APPEALS

 FOR THE NINTH CIRCUIT

MICHAEL D. NELSON,

 Plaintiff - Appellant,

 v.

MATRIXX INITIATIVES, INC., a

Delaware corporation and ZICAM, LLC,

an Arizona limited liability company,

 Defendants - Appellees.

No. 12-17455

D.C. No. 3:09-cv-02904-WHA

MEMORANDUM*

Appeal from the United States District Court

for the Northern District of California

William Alsup, District Judge, Presiding

Submitted January 16, 2015** 

San Francisco California

Before: WALLACE, M. SMITH, and FRIEDLAND, Circuit Judges.

Michael Nelson appeals from the district court’s orders excluding Nelson’s

two expert witnesses on specific causation, and granting Matrixx’s motion for

FILED

FEB 02 2015

MOLLY C. DWYER, CLERK

U.S. COURT OF APPEALS

 * This disposition is not appropriate for publication and is not precedent

except as provided by 9th Cir. R. 36-3.

 ** The panel unanimously concludes this case is suitable for decision

without oral argument. See Fed. R. App. P. 34(a)(2).
summary judgment. Because the parties are familiar with the facts and procedural

history of this case, we repeat only those facts necessary to resolve the issues

raised on appeal. We affirm.

In a toxic tort case in California, a plaintiff must show both general

causation, which is “that the substance at issue was capable of causing the injury

alleged,” and specific causation, which is “that the substance caused, or was a

substantial factor in causing, the specific plaintiff’s injury.” Avila v. Willits Envtl.

Remediation Trust, 633 F.3d 828, 836 (9th Cir. 2011) (citing Jones v. Ortho

Pharm. Corp., 209 Cal. Rptr. 456, 462 (Cal. Ct. App. 1985)). General and specific

causation “must be proven within a reasonable medical probability based upon

competent expert testimony.” Jones, 209 Cal. Rptr. at 460. 

Nelson offered Drs. Davis and Hwang as experts on the issue of specific

causation, and both Drs. Davis and Hwang relied on differential diagnosis for their

expert opinions that Nelson’s smell loss was caused by Zicam. “Differential

diagnosis is a common scientific technique, and federal courts, generally speaking,

have recognized that a properly conducted differential diagnosis is admissible

under Daubert.” Clausen v. M/V New Carissa, 339 F.3d 1049, 1057 (9th Cir.

2003). However, “expert testimony that neglects to consider a hypothesis that

might explain the clinical findings under consideration may also be unreliable.” Id.

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at 1058. Elimination of the potential causes “must be founded on more than

‘subjective beliefs or unsupported speculation.’” Id. (quoting Claar v. Burlington

N. R.R. Co., 29 F.3d 499, 502 (9th Cir. 1994)). 

The district court excluded Dr. Davis’s testimony and expert report, and Dr.

Hwang’s testimony, because it found that neither expert was able to provide a

reliable method for ruling in Zicam, or ruling out age or the cold virus as the cause

of Nelson’s smell loss. As the district court states, “[b]oth age and the cold virus

are well-established, common causes of smell loss.” The district court did not

abuse its discretion in concluding that Nelson’s two expert witnesses were not

sufficiently reliable on the issue of specific causation, and in excluding both

experts on that basis. 

After excluding Drs. Davis and Hwang, the court granted Matrixx’s motion

for summary judgment because Nelson had provided no additional expert

testimony on the issue of specific causation and therefore could not prove a

necessary element in his case. Without any reliable expert witness testimony on

specific causation, the district court correctly granted Matrixx’s motion for

summary judgment. 

Finally, because none of Nelson’s remaining arguments find support in

either the facts or law, the district court correctly declined to shift the burden of

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proving causation to Matrixx, correctly precluded reliance on FDA action or

discovery of third party medical histories, and correctly rejected Nelson’s claim to

recover the purchase price of Zicam.

AFFIRMED.

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