I agree that there is “no per se or categorical bar” to the class treatment of medical monitoring claims (lead opn., ante, at p. 1105), and that there are some common issues (see lead opn., ante, at pp. 1106-1108). I also agree that “the trial court *1112abused its discretion in granting the instant certification motion” because plaintiffs failed to establish that the common issues predominate. (Id. at p. 1111.) Thus, I join in parts I and II of the lead opinion and its disposition. I, however, cannot join part III of the lead opinion because it fails to adequately convey the complexity of plaintiffs’ claims and, as a result, fails to acknowledge many of the individual issues that must be resolved in order to decide the proposed class action. Indeed, upon considering the full breadth of plaintiffs’ claims in light of the record, I do not believe any court could reasonably conclude that they are suitable for class treatment.
I
To fully appreciate the complexity of plaintiffs’ proposed class action, I recount in greater detail the relevant facts.
In 1954, Grand Central Rocket Company (GCRC) constructed a facility used for the production, testing and disposal of rocket propellants (the rocket facility) in the Redlands/Crafton area. In 1958, defendant Petro-Tex Chemical Corporation (Petro-Tex)—which was jointly owned by defendants Food Machinery and Chemical Corporation (FMC) and Tennessee Gas Transmission Corporation (now El Paso Tennessee Pipeline Co.; Tenneco)—acquired GCRC and the rocket facility. In a series of transactions from 1960 to 1961, defendant Lockheed Martin Corporation (Lockheed) acquired GCRC and the facility. Lockheed manufactured, assembled and tested solid fuel rockets at the facility—which covered approximately 400 acres—until 1974. From the opening of the rocket facility in 1954 to its closing in 1974, these defendants discharged toxic substances throughout the facility’s 400-acre property and contaminated the water used by surrounding residents.
In 1979, Lockheed leased 66 acres of the property to Seven W Enterprises, Inc. (Seven W). Seven W then acquired another 24 acres of adjacent property from the City of Redlands and constructed an industrial park. Since the creation of this park, tenants—specifically, defendants Baumac Corporation (Baumac), Highland Supply Corporation (Highland) and Palco Communications, Inc. (Palco)—have discharged toxic substances around the park and further contaminated the water used by surrounding residents.
As a result of this discharge of toxic substances, plaintiffs filed this class action against seven defendants—Petro-Tex, FMC, Tenneco, Lockheed, Baumac, Highland and Palco. Plaintiffs did not seek compensatory damages. Instead, they limited their recovery to “[sjpecial damages ... to establish a fund for periodic medical monitoring and medical testing for each Plaintiff and Class member” and “punitive and exemplary damages.” Consistent with *1113this limitation, plaintiffs identified two potential classes—a medical monitoring class and a punitive damages class.
In their motion to certify, plaintiffs defined the class as “[p]eople who were exposed to water contaminated with” certain toxic substances “at levels at or in excess of the dose equivalent of the MCL (Maximum Contaminant Level), or in excess of the safe dose where there is no MCL, for some part of a day, for greater than 50% of a year, for one or more years from 1955 to the present, within” certain “geographical boundaries” which encompassed the City of Redlands. Plaintiffs estimated the class contained 50,000 to 100,000 members and identified over 12 toxic substances discharged by defendants, including TCE, PCE, TCA, ammonium perchlorate, perchlorate, beryllium, carbon tetrachloride, vinyl chloride, hydrazine (and hydrazine derivatives), nitrosamines (and nitrosamine derivatives), epoxides (and epoxide derivatives) and triazines (and triazine derivatives). Plaintiffs also identified over 40 different medical conditions that may require medical monitoring due to exposure to those substances.1
The trial court certified both the medical monitoring and punitive damages classes. The Court of Appeal reversed, concluding that the individual issues raised by plaintiffs’ claims “clearly predominate” over the common issues.
II
Plaintiffs seek to certify a class consisting of all people exposed to a specified dose of one of at least 12 different toxic substances for a certain period of time from 1955 to the present, within a geographical area encompassing the City of Redlands. They allege that each class member—estimated to number 50,000 to 100,000—may require medical monitoring for over 40 medical conditions. Plaintiffs seek to recover medical monitoring damages from seven different defendants that dumped these chemicals in *1114various locations on a 400-plus-acre property over a time period of 40-plus years. Given the size and complexity of these class claims, I do not believe a court could reasonably conclude that the common issues predominate and certify the proposed class.
“[T]he cost of medical monitoring is a compensable item of damages where the proofs demonstrate, through reliable medical expert testimony, that the need for future monitoring is a reasonably certain consequence of a plaintiffs toxic exposure and that the recommended monitoring is reasonable.” (Potter v. Firestone Tire & Rubber Co. (1993) 6 Cal.4th 965, 1009 [25 Cal.Rptr.2d 550, 863 P.2d 795] (Potter)) Under this standard, a plaintiff may not obtain medical monitoring “based ‘solely upon a showing of an increased but unquantified risk resulting from exposure to toxic chemicals.’ ” (Ibid.) Rather, “toxic exposure plaintiffs may recover ‘only if the evidence establishes the necessity, as a direct consequence of the exposure in issue, for specific monitoring beyond that which an individual should pursue as a matter of general good sense and foresight.’” (Ibid., italics added.) The availability of monitoring therefore depends on the particular need of a particular plaintiff. (See ibid.)
Thus, a member of plaintiffs’ proposed class may obtain medical monitoring damages for a medical condition only if that member’s exposure to the chemicals dumped by defendants necessitate more monitoring than he or she would otherwise need. (See Potter, supra, 6 Cal.4th at p. 1009.) To order additional medical monitoring, a trier of fact must therefore determine (1) the extent of monitoring that the class member would have required for that medical condition absent exposure; and (2) whether the class member needs any additional monitoring due to exposure to the substances discharged by defendants.
Applying this standard of causation, the majority concludes that “the medical expert testimony plaintiffs presented in support of their motion for class certification is too qualified, tentative and conclusionary to constitute substantial evidence that plaintiffs, by adopting a liability theory that makes actual dosages and variations in individual response irrelevant, will be able to prove causation and damages by common evidence.” (Lead opn., ante, at p. 1111.) In reaching this conclusion, the majority focuses on plaintiffs’ failure to show that dosages issues and the need for medical monitoring are susceptible to common proof. (See lead opn., ante, at pp. 1109-1 111.) I agree with the majority so far as it goes. But the majority fails to fully consider the extraordinary complexity of plaintiffs’ claims in its analysis and, as a result, understates the deficiencies of plaintiff’s showing in support of class certification.
*1115As a threshold matter, determining each defendant’s liability to the class for medical monitoring damages requires the resolution of a staggering number of complex individual issues. First, determining the extent of monitoring required by each class member absent exposure poses a highly individualized inquiry. A class member’s risk of developing a medical condition depends on numerous factors unique to that member, such as age, gender, lifestyle, fitness, preexisting conditions, exposure to hazardous substances not released by defendants, etc. Given that plaintiffs identify over 40 medical conditions that may necessitate additional monitoring for approximately 50,000 to 100,000 individuals, the number and complexity of these individual determinations is overwhelming.
Second, determining whether each class member requires additional monitoring due to exposure requires individual litigation of numerous and substantial questions. A class member’s need for additional monitoring hinges on the particular traits or characteristics of each class member. As plaintiffs’ own experts acknowledge, human reaction to environmental and other hazards varies from individual to individual. It is directly affected not only by the individual’s dosage or extent of exposure, but also by preexisting conditions, genetic makeup, age, gender, size, nutrition, adaptation and acclimatization to geographic and climatological factors, lifestyle, family history, social history, occupational history and personal health history. Thus, whether an individual class member needs additional medical monitoring depends heavily on numerous factors specific to that individual—and not just the dosage of toxic substances received. Moreover, the clinical value of early detection and diagnosis may vary significantly depending on the medical condition at issue and the individual characteristics of each class member. Given the number of hazardous substances involved, the number of medical conditions implicated, and the size of the class, resolution of the many individual issues necessary to establish each individual class member’s entitlement to additional monitoring due to exposure would be a herculean task. Because determining “the basic issue of defendant[s’] liability to the purported class” requires the resolution of countless issues specific to each class member, class treatment is not appropriate. (City of San Jose v. Superior Court (1974) 12 Cal.3d 447, 463 [115 Cal.Rptr. 797, 525 P.2d 701, 76 A.L.R.3d 1223] (City of San Jose))
Aside from the individualized inquiries necessary to establish liability, the individualized inquiries necessary to establish the extent of additional medical monitoring required by those class members who prove liability are also numerous and substantial. To determine the extent of monitoring required, the court would have to ascertain the significance and extent of each member’s exposure to the chemicals dumped by defendants. Because of the *1116number of chemicals involved, their potential synergistic effects, the duration of dumping, the size of the area in which the dumping occurred, and the intricacies of hydrogeology, this task depends on the resolution of numerous questions specific to each class member. Consequently, individual questions dominate such a determination. Finally, the resolution of various affirmative defenses—i.e., statute of limitations—also requires separate adjudication for each class member.
Viewed altogether, the individual questions that must be resolved in order to resolve plaintiffs’ claims are staggering in both number and complexity. Indeed, “subsequent to the rendering of any class judgment which determined in plaintiffs’ favor whatever questions were common to the class,” the trial court in this case would have to conduct tens of thousands of complex individualized trials over causation, damages and affirmative defenses. (Vasquez v. Superior Court (1971) 4 Cal.3d 800, 809 [94 Cal.Rptr. 796, 484 P.2d 964, 53 A.L.R.3d 513].) Invocation of the class action mechanism under these circumstances would not promote efficiency. Rather, it would “deprive either the defendants] or the members of the class—or both—of a fair trial.” (See City of San Jose, supra, 12 Cal.3d at p. 462.)
The possible creation of subclasses makes no difference in this case. While subclasses may sufficiently minimize the individual issues in certain cases, we have long recognized that “there are limits outside of which the subclassification system ceases to perform a sufficiently useful function to justify the maintenance of the class action.” (City of San Jose, supra, 12 Cal.3d at p. 463, fn. 10.) This is such a case. Plaintiffs allege that seven different defendants dumped over 12 chemicals at multiple locations on a 400-plus-acre property over 40-plus years. In doing so, these defendants allegedly harmed 50,000 to 100,000 people with different characteristics by placing them at greater risk for contracting over 40 possible medical conditions. “Given the number of variables involved in this case,” the potential number of subclasses is mind-boggling. (Kennedy v. Baxter Healthcare Corp. (1996) 43 Cal.App.4th 799, 813 [50 Cal.Rptr.2d 736].) Class certification under these facts would therefore defeat “the purposes served by class action litigation.” (Ibid.)
In this respect, O’Connor v. Boeing North American, Inc. (C.D.Cal. 2000) 197 F.R.D. 404 (O’Connor II) is instructive. In O’Connor v. Boeing North American, Inc. (C.D.Cal. 1998) 184 F.R.D. 311, 316 (O’Connor I) and O’Connor II, the plaintiffs alleged that the defendants discharged radioactive and nonradioactive hazardous substances at four facilities. (See O’Connor I, at p. 316.) This discharge allegedly created a continuing health hazard for people living near these facilities. (Id. at pp. 316-317.) The plaintiffs sought *1117to certify three classes. As relevant here, class I consisted of “ ‘[a]ll persons: (1) who presently reside or work in the Contamination Area or who, at any time since 1946, have resided or worked in the Contamination Area; and (2) who have not been diagnosed with a type of cancer or other serious illness or disease which may be attributed to exposure to the radioactive contaminants and/or hazardous, non-radioactive substances released from’ ” the facilities. (Id. at p. 317.) Like plaintiffs, the O’Connor plaintiffs sought to establish a medical monitoring program for the class funded by the defendants. (Ibid.)
Although the federal district court initially certified the medical monitoring class (see O’Connor I, supra, 184 F.R.D. at p. 339), it later decertified the class (see O’Connor II, supra, 197 F.R.D. at p. 413). In doing so, the court not only cited the “individualized focus of the statute of limitations defense” (ibid.), but also admitted that it had “underestimated the difficulty of applying the individualized factors required by” Potter “to the Class I medical monitoring claim in its” order certifying the class (id. at p. 413, fn. 6).
These conclusions are especially cogent in this case, given that plaintiffs’ class claims and the class claims in O’Connor II are analogous in their breadth and complexity. Moreover, the reasoning of the court in O’Connor II is even more persuasive here because plaintiffs’ proposed medical monitoring class is even broader than the class proposed in O'Connor II. (See O’Connor I, supra, 184 F.R.D. at p. 317 [the plaintiffs’ class expressly excluded those persons who have been diagnosed with a medical condition attributable to exposure].) Indeed, other courts have refused to certify medical monitoring classes in analogous cases using similar reasoning. (See, e.g., Goasdone v. American Cyanamid (2002) 354 N.J.Super. 519 [808 A.2d 159, 172-173] (Goasdone) [refusing to certify a medical monitoring class consisting of all people who worked at a textile plant for 30 days or more from 1946 until 1983 and were exposed to benzidine-related dyes resulting in an increased risk of contracting bladder cancer because the individual issues predominated].)
The federal cases cited by plaintiffs in support of class certification are inapposite. Even assuming these cases are still persuasive (see Goasdone, supra, 808 A.2d at p. 169), all of them involved simpler facts and claims.2 By contrast, plaintiffs’ class claims are incredibly complex even for a mass *1118tort action. Permitting certification under these facts would, as a practical matter, make all medical monitoring claims subject to class treatment. Such a result would open the “floodgates of litigation” notwithstanding our carefully crafted decision in Potter. (Potter, supra, 6 Cal.4th at p. 1009.) Rather than do so, I believe other procedures traditionally used to manage complex litigation, like consolidation and coordination, may be more appropriate. (See Rose v. Medtronics, Inc. (1980) 107 Cal.App.3d 150, 155 [166 Cal.Rptr. 16] [“consolidation of actions is the preferred procedure for disposition of’ mass tort cases].)
Accordingly, I join the lead opinion in affirming the judgment of the Court of Appeal.
Baxter, J., and Chin, J., concurred.
According to plaintiffs, exposure to these substances may increase the risk for developing the following medical conditions: “1. Cancer of all types. 2. Respiratory effects including asthma, CORD, rhinitis, sinusitis, and bronchitis. 3. Neurological deficits including headache syndromes, encephalopathy, neuropathy, movement disorders, color blindness, learning disabilities and emotion lability. 4. Reproductive damage including sperm damage, miscarriages, infertility and birth defects. 5. Immunologic problems including scleroderma, systemic lupus, erythematosis, rheumatoid arthritis, Raynaud’s phenomenon, inflammatory bowel disease, mixed connective tissue disease and fibromyalgia. 6. Neuroendocrine dysregulation including hypothyroidism, menstrual irregularities, decreased libido, chronic fatigue syndrome and multiple chemical sensitivity. 7. Psychiatric problems including post traumatic stress disorder, depression and anxiety. 8. Skin problems including eczema, chloracne, contact dermatitis, defatting dermatitis and allergic dermatitis. 9. Cardiac effects including arteriosclerosis, dysrhythmias, cardiac malformations and cardiomyopathy. 10. Hematologic damage including thrombocytopenia, anemia and leukopenia.”
(See, e.g., Friends for All Children v. Lockheed Aircraft (D.C. Cir. 1984) 746 F.2d 816, 819-820 [46 A.L.R.4th 1113] [alleging that a single defendant negligently manufactured an aircraft that crashed, potentially causing a single neurological development disorder in no more than 149 children and seeking the creation of a medical monitoring fund for approximately 40 children]; Day v. NLO (S.D. Ohio 1994) 851 F.Supp. 869, 874-875 [alleging that a plant exposed visitors and workers to hazardous materials and seeking to certify a class of *1118“workers and frequenters” to the plant]; Yslava v. Hughes Aircraft Co. (D.Ariz. 1993) 845 F.Supp. 705, 707-708, 712 [alleging that a single defendant disposed of hazardous wastes in a single location over 29 years and identifying “24 separate subgroups representing precise geographic areas where plaintiffs lived, worked or went to school”]; Boggs v. Divested Atomic Corp. (S.D. Ohio 1991) 141 F.R.D. 58, 60-62 [alleging that a single plant released radioactive substances and seeking to certify a class numbering in the thousands of persons “who were residents, property owners or lessees of property within a radius of six miles from” the plant]; but see Boggs v. Divested Atomic Corp. (S.D. Ohio, Mar. 24, 1997, No. C-2-90-840) 1997 WL 33377790 [subsequently decertifying the class].)