I concur in the majority’s conclusion that plaintiffs may recover from Firestone for the emotional distress they have suffered as a result of their fear of developing cancer because of Firestone’s egregious misconduct in the disposal of its toxic waste. I dissent, however, from the majority opinion insofar as it holds that plaintiffs would not be entitled to recover for their emotional distress had defendant simply been negligent in contaminating plaintiffs’ water supply.
As I shall explain, I believe the majority opinion has departed from well-established tort principles—long recognized in California—in holding that, when a defendant negligently contaminates another person’s water supply, subjecting that person to the risk of personal injury or illness, the victim of this contamination may recover for the emotional distress reasonably suffered by the fear of incurring such injury or illness only if the victim can establish that he or she is "more likely than not” to develop the injury or illness.
As the majority opinion recognizes, a reasonable person who has consumed, cooked with, and bathed in water that has been contaminated by toxic waste is likely to sustain serious emotional distress relating to the fear of developing a serious illness in the future, not only when the person’s chance of developing an illness is more than 50 percent, but also when his or her chance of developing the illness is considerably lower, for example, “only” 25 or 30 percent. In denying recovery to such a victim, despite the circumstance that—because of the risk of personal harm engendered by the defendant’s negligent conduct—a person of ordinary sensibilities in the victim’s position reasonably would suffer serious emotional distress, the majority opinion eliminates an important legal protection to which all persons, including victims of toxic waste exposure, long have been entitled.
In explaining its rationale for establishing a novel, high threshold—“more likely than not”—for recovery for emotional distress in this setting, the majority opinion suggests that, in the case of “toxic torts,” a variety of “public policy” reasons support its departure from generally governing legal *1020principles. Distilled to its essence, however, the majority’s position amounts to a determination that, when a defendant’s wrongful conduct has the potential to cause serious physical and emotional harm to a large number of persons, such conduct should be afforded a greater shield from liability than conduct possessing the potential to harm only a more limited number of persons. In my view, the controlling public policy formulated in this area— for example, the stringent legislative controls governing the discarding of toxic waste—does not support the majority’s approach. Indeed, it appears distressingly ironic and inconsistent with legislatively prescribed public policy to accord the individual victim of a so-called “toxic tort” less protection than would be accorded the victim of a more traditional course of negligent conduct.
In past decisions, this court has taken into account the danger that potentially disproportionate liability might be imposed when the issue presented was whether, and under what circumstances, a defendant who negligently injured one person should be held liable for the emotional distress suffered by other persons by reason of their concern over the condition of the injured person. The majority opinion in the present case, however, is the first to invoke such a rationale to limit recovery by persons who, as result of a defendant’s negligence, have been made to suffer the risk of personal physical injury or illness and who, as a consequence, reasonably have incurred emotional distress arising out of concern for their own health and safety. I believe there is no justification for limiting the recovery to which this class of persons is entitled, simply because the defendant’s wrongful conduct has endangered the personal safety of a large number of invididuals.
Finally, the majority’s determination to embrace this novel, restrictive approach is all the more difficult to understand in that the majority’s formulation is at odds with most of the decisions from other jurisdictions that have addressed this very issue in the arena of toxic torts and fear of cancer. As discussed below, numerous federal and sister-state decisions demonstrate that the policy reasons offered by the majority in support of its “more likely than not” threshold standard appropriately may be invoked when a plaintiff seeks compensation for what, in contrast, are essentially future damages (e.g., future medical expenses, loss of earnings, diminished life expectancy), for an illness or disease that may (or may not) develop in the future. As these out-of-state decisions explain, however, considerations such as those invoked by the majority do not justify the adoption of a stringent standard when a plaintiff simply seeks to recover present damages for the serious emotional distress that he or she already has suffered, reasonably and foreseeably, because of the substantial risk to the plaintiff’s health posed by the defendant’s negligence.
*1021In sum, in my view no sound basis exists for the majority’s adoption of a completely novel approach narrowly limiting the circumstances under which a person—whose water supply has been contaminated as a result of a defendant’s negligent disposal of toxic waste—may recover for the serious emotional distress that he or she reasonably has suffered.
I
Well over half a century ago, this court recognized a plaintiff’s right to recover damages for fright, shock, and nervous distress when the negligent conduct of a defendant places the plaintiff personally at risk, causing the plaintiff reasonably to fear for his or her own safety, even in the absence of any injurious impact. (See, e.g., Webb v. Francis J. Lewald Coal Co. (1931) 214 Cal. 182 [4 P.2d 532, 77 A.L.R. 675]; Lindley v. Knowlton (1918) 179 Cal. 298 [176 P. 440]; Vanoni v. Western Airlines (1967) 247 Cal.App.2d 793 [56 Cal.Rptr. 115]; see also Dillon v. Legg (1968) 68 Cal.2d 728, 738, fn. 4 [69 Cal.Rptr. 72, 441 P.2d 912, 29 A.L.R.3d 1316] [citing “California’s rule that plaintiff’s fear for his own safety is compensable”].)
Thus, for example, if an automobile driver negligently speeds by a pedestrian in a crosswalk, narrowly missing the pedestrian but causing him or her reasonably to suffer serious emotional distress as a result of the encounter, the pedestrian is entitled to recover damages for reasonable emotional distress, even though the driver’s conduct, while posing a risk of personal harm to the pedestrian, did not in fact inflict any direct physical injury. As this example illustrates, under traditional negligence principles a plaintiff’s right to recover damages for emotional distress sustained as a result of fear or concern for his or her own health and safety does not depend upon whether the plaintiff actually incurred a physical injury (or disease) as a result of the defendant’s conduct. Rather, so long as the defendant has breached a duty of care owed to the plaintiff, thereby subjecting the plaintiff to an unreasonable risk of personal injury or illness, and the defendant’s conduct is of such a nature that a reasonable person, in the plaintiff’s position, would sustain serious emotional distress as a result of such conduct, the plaintiff who in fact sustains such emotional distress generally is entitled to recover damages for that distress.1
In the present case, Firestone’s wrongful dumping of toxic substances resulted in the contamination of plaintiffs’ property and well water, and led *1022directly to plaintiffs’ involuntary and unknowing ingestion of carcinogens (including benzene and vinyl chloride, substances known to cause chromosomal damage and to have deleterious effects upon the central nervous amd immune systems) over a prolonged period of time, in amounts greatly exceeding levels deemed acceptable by the federal Environmental Protection Agency. Indisputably, therefore, Firestone’s conduct subjected plaintiffs directly to a foreseeable risk of personal harm—the risk of developing cancer or some other disease as the result of the ingestion of such substances. Because they were subjected by Firestone’s conduct to this risk of personal harm, plaintiffs incurred serious emotional distress arising out of concern for their own health and safety.
Under these circumstances, the general tort principle set forth above— authorizing recovery for emotional distress when a plaintiff is personally endangered by a defendant’s negligent conduct and suffers serious emotional distress out of fear for his or her own safety—directly supports plaintiffs’ right to recover damages for the serious emotional distress they reasonably sustained, emanating from concern for their own health.
Furthermore, past decisions of this court—applying general principles from the law of nuisance and trespass—similarly have held that, when a defendant tortiously interferes with the water supply to another person’s property, the person whose water supply has been impaired is entitled to recover for emotional distress resulting from the tortious conduct, without regard to whether he or she has sustained any actual physical injury. As this court explicitly declared in Acadia, California, Ltd. v. Herbert (1960) 54 Cal.2d 328, 337 [5 Cal.Rptr. 686, 353 P.2d 294], a case involving the wrongful interference with another person’s water supply: “It is settled that, regardless of whether the occupant of land has sustained physical injury, he may recover damages for the discomfort and annoyance of himself and the members of his family and for mental suffering occasioned by fear for the safety of himself and his family when such discomfort or suffering has been proximately caused by a trespass or nuisance.” (Italics added; see Kornoff v. Kingsburg Cotton Oil Co. (1955) 45 Cal.2d 265, 272 [288 P.2d 507] [plaintiffs’ suffering caused by fear for their safety was a natural consequence of defendant’s invasion of their property and therefore was a recoverable item of damages]; Herzog v. Grosso (1953) 41 Cal.2d 219, 225-226 [259 P.2d 429].)
*1023In light of these well-established principles of tort law, I believe the trial court properly concluded that, because a reasonable person in plaintiffs’ position likely would sustain serious emotional distress arising from concern over the risk that defendant’s conduct posed to the person’s own health, plaintiffs were entitled to recover damages for the emotional distress they in fact suffered.
II
The majority acknowledges that Firestone, in negligently disposing of its toxic waste at a facility from which such waste was banned, breached the duty of care it owed to plaintiffs, who resided on property in the vicinity of the site of the waste disposal. And the majority also acknowledges that a reasonable person whose water supply has been contaminated by toxic waste is likely to suffer serious emotional distress arising out of fear for his or her own health, even though there is considerably less than a 50 percent likelihood that the toxic waste to which the victim was exposed will in fact cause him or her to contract cancer or some other serious disease. Nonetheless, the majority deliberately limits the class of persons who can recover for the serious emotional distress they have suffered to the very small class of persons who can prove it is “more likely than not” that they will contract such a disease as a result of the defendant’s conduct, denying recovery to the much greater number of persons who have sustained serious emotional distress but who have “only,” for example, a 25 or 30 percent chance of contracting the disease.
As noted earlier, the majority cites a variety of “public policy” considerations in support of its “more likely than not” standard, arguing that a less stringent standard will result in a potentially unrestricted plaintiff class at a “tremendous societal cost” that, in turn, will (1) limit the availability and affordability of liability insurance for toxic liability risks, and (2) impede access to prescription drugs because of a possible proliferation of “fear of cancer” claims by the users of such medications. But these reasons amount to no more than an asserted need to restrict the potential “unlimited” liability that otherwise might burden a “toxic tort” defendant, because of the number of persons who may be adversely affected by the improper handling of toxic waste. Thus, the essence of the policy reasons invoked by the majority is a fear that, in toxic tort cases, negligent defendants may have endangered so many persons that permitting recovery under ordinary negligence standards may impose an onerous risk of liability upon these defendants. Under well-established negligence principles, however, a defendant’s liability for a particular category of negligent conduct does not contract as the number of persons injured increases. In my view, it is unfair to plaintiffs in the present *1024case to impose upon them a threshold standard for recovery that is much more stringent than would apply had Firestone’s negligent conduct had the potential to contaminate the well water of only a single property owner.
Past decisions limiting the class of persons who may recover damages for emotional distress generally have involved claimants who have suffered by reason of an injury caused to another person. (See, e.g., Thing v. La Chusa (1989) 48 Cal.3d 644, 661-668 [257 Cal.Rptr. 865, 771 P.2d 814]; Elden v. Sheldon (1988) 46 Cal.3d 267, 211 [250 Cal.Rptr. 254, 758 P.2d 582].) In these cases, the courts found it appropriate to establish definite limitations upon the potential class of plaintiffs, recognizing that imposing liability upon a negligent defendant who injures a person, for the emotional distress suffered by other persons as a result of that single injury, frequently will magnify liability well out of proportion to culpability.
These concerns are inapplicable in the present case, however, where the potential class of plaintiffs is limited to those persons who directly and personally were placed at risk by Firestone’s negligent course of conduct. In other situations in which a defendant’s negligence has injured or placed at risk a large number of persons (for example in an airplane crash or in other “mass tort” settings), we have not limited recovery for damages for emotional distress that reasonably has been suffered by those persons.
Indeed, in cases in which a plaintiff seeks to recover for emotional distress relating to fear for his or her own safety, there is no need to create a novel, artificial barrier in order to avoid an unwarranted expansion of emotional distress claims—as the majority opinion does in adopting its “more likely than not” standard—because reasonable restraints upon such claims already are subsumed under negligence principles generally applicable in this area of the law. As previously explained, to be entitled to recover such damages in these circumstances, a plaintiff must demonstrate not merely that he or she suffered some degree of emotional distress, but rather that the distress rose to the level of serious emotional distress. (Molien v. Kaiser Foundation Hospitals, supra, 21 Cal.3d at pp. 928-930; Burgess v. Superior Court (1992) 2 Cal.4th 1064, 1073, fn. 6 [9 Cal.Rptr.2d 615, 831 P.2d 1197].) Additionally, to justify recovery, a plaintiff must establish not only that he or she suffered this high level of emotional distress, but also that the circumstances are such that a reasonable person, in the plaintiff’s position, would be likely to suffer that degree of distress, i.e., that the circumstances are such that “ ‘a reasonable [person], normally constituted, would be unable to adequately cope with the mental stress engendered by the circumstances of the case.’ [Citation.].” (Molien, supra, 21 Cal.3d at p. 928.) Finally, the plaintiff must demonstrate that the circumstances that generated the serious emotional distress were proximately caused by the defendant’s negligent conduct.
*1025In my view, in applying these generally applicable principles in the context of toxic exposure, an appropriate threshold standard would require that, in order to be entitled to recover for emotional distress, a plaintiff establish not only that he or she in fact sustained serious emotional distress, but also that (1) the level of toxic substances to which he or she was exposed posed a significant risk that the plaintiff will develop the feared disease or illness (i.e., a risk that is sufficiently substantial that it would result in serious emotional distress in a reasonable, rather than an unusually sensitive, person), and (2) the defendant’s negligence substantially increased plaintiff’s risk of contracting the disease or illness (so that the plaintiff’s serious emotional distress is a condition for which the defendant appropriately should be held responsible.)
I note that we have affirmed the reliability of the “substantial” factor test as a means of establishing and delimiting liability in other contexts of tort law. For example, in Mitchell v. Gonzales (1991) 54 Cal.3d 1041, 1052 [1 Cal.Rptr.2d 913, 819 P.2d 872], in approving BAJI No. 3.76, employing the “substantial factor” test of causation in fact, we observed: “[T]he ‘substantial factor’ test,” developed by the Restatement Second of Torts, section 431, and incorporated in BAJI No. 3.76, “has been comparatively free of criticism and has even received praise. ‘As an instruction submitting the question of causation in fact to the jury in intelligible form, it appears impossible to improve on the Restatement’s “substantial factor [test.]” ’ [Citation.] It is ‘sufficiently intelligible to any layman to furnish an adequate guide to the jury, and it is neither possible nor desirable to reduce it to lower terms.’ ”
In sum, because the generally applicable tort principles have been fashioned so as to avoid imposition of unlimited or undue liability for emotional distress claims made by persons who physically have been endangered by a defendant’s negligent conduct, there is, in my opinion, no justification for the majority opinion’s holding saddling direct victims of toxic exposure with an additional and onerous “more likely than not” standard, a threshold that, as a practical matter, is likely to constitute a barrier barring recovery for even the most extreme and reasonably sustained emotional distress, in virtually all cases in which a disease possessing a lengthy latency period has not yet manifested itself.
Ill
In adopting a “more likely than not” standard as a severe limitation upon the right of toxic-tort victims to obtain compensation for the emotional distress they reasonably and foreseeably suffer as a result of concern for their health and safety, the majority opinion declines to follow a substantial *1026body of decisions from other jurisdictions that have addressed this very issue.
Numerous federal and out-of-state authorities recognize that the tort of negligent exposure to toxic substances gives rise to two completely distinct types of claims for compensatory damages: (1) one involving the increased risk of developing a disease in the future, and (2) the other, typified in the case before us, involving the present injury of emotional distress, engendered by the claimant’s knowledge that he or she has ingested a harmful substance (referred to as a claim premised upon “fear of cancer”). The United States Sixth Circuit Court of Appeals recently stated: “A real distinction can be drawn between the possibility of recovery for increased risk of cancer and that for increased fear of cancer .... [Fear of cancer] is a claimed present injury consisting of mental anxiety and distress over contracting cancer in the future, as opposed to increased risk of cancer, which is a potential physical predisposition of developing cancer in the future.” (Cantrell v. GAF Corp. (6th Cir. 1993) 999 F.2d. 1007, 1012.)
Almost without exception, courts have required, as a prerequisite to recovery on an “increased risk” claim, that the plaintiff establish “to a reasonable medical certainty”—or that it is “more likely than not”—that the plaintiff actually will develop the disease in the future. (See, e.g., Abuan v. General Electric Co. (9th Cir. 1993) 3 F.3d 329, 334; Sterling v. Velsicol Chemical Corp. (6th Cir. 1988) 855 F.2d 1188, 1204-1206; Dartez v. Fibreboard Corp. (5th Cir. 1985) 765 F.2d 456, 466.)
With respect to a claim for emotional distress involving fear of cancer, however, the majority of jurisdictions and legal commentators recognize that a “more likely than not” threshold standard is not applicable; rather, a plaintiff’s likelihood of actually developing the feared disease simply is one relevant factor in assessing the reasonableness of his or her claim. (See Cantrell v. GAF Corp., supra, 999 F.2d at p. 1012; Sterling v. Velsicol Chemical Corp., supra, 855 F.2d 1188; Dartez v. Fibreboard Corp., supra, 765 F.2d at p. 468; Hagerty v. L & L Marine Services, Inc. (5th Cir. 1986) 788 F.2d 315, 318, mod. on denial of rehg. en banc, (1986) 797 F.2d 256; Merry v. Westinghouse Electric Corp. (M.D. Pa. 1988) 684 F.Supp. 847, 852; Lavelle v. Owens-Coming Fiberglas Corp. (1987) 30 Ohio Misc.2d 11 [507 N.E.2d 476]; see also In re Moorenovich (D.Me. 1986) 634 F.Supp. 634.)
This now well-accepted principle was stated in Sterling v. Velsicol Chemical Corp., supra, 855 F.2d at page 1206, as follows: “While there must be a reasonable connection between the injured plaintiff’s mental anguish and the *1027prediction of a future disease, the central focus of a court’s inquiry in such a case is not on the underlying odds that the future disease will in fact materialize. To this extent, mental anguish resulting from the chance that an existing injury will lead to the materialization of a future disease may be an element of recovery even though the underlying future prospect for susceptibility to a future disease is not, in and of itself, compensable inasmusch as it is not sufficiently likely to occur.” (Italics added.)
Following an extensive review of decisions in other jurisdictions, the authors Schwartzbauer and Shindell, in Cancer and the Adjudicative Process: The Interface of Environmental Protection and Toxic Tort Law (1988) 14 Am.J.L. & Med. 1, conclude at page 43: “If the anxiety is both genuine and non-trivial, a plaintiff ought not be denied a recovery merely because the chance that the future consequence will develop is forty-nine percent rather than fifty-one percent. The ‘more-likely-than not’ test is used to determine whether to compensate for the future consequence itself; not for the present fear of such a future consequence.” (Italics added.)
IV
The majority’s creation of a novel, unrealistically high threshold standard for recovery for serious emotional distress, reasonably and foreseeably suffered by plaintiffs as the result of Firestone’s negligent contamination of their well water, constitutes an unwarranted deviation from tort principles well established under the decisional law of California and other jurisdictions. In my view, this deviation is directly contrary to, rather than in furtherance of, established public policy in the area of toxic exposure.
Accordingly, I would affirm the trial court’s award of emotional distress damages in favor of plaintiffs.
In Molieti v. Kaiser Foundation Hospitals (1980) 27 Cal.3d 916 [167 Cal.Rptr. 831, 616 P.2d 813, 16 A.L.R.4th 518], this court concluded that, in some circumstances, a plaintiff may recover for emotional distress, unaccompanied by any physical manifestation of injury, even when the defendant’s negligent conduct does not subject the plaintiff to a risk of physical injury or disease but instead subjects the plaintiff, as a “direct victim,” to the risk of serious emotional distress. In the present case, of course, defendant’s conduct subjected plaintiffs to the risk of physical injury or illness, and thus it is clear under the cases cited above—decided *1022long before Molien—that these plaintiffs fall within the class of persons who traditionally have been permitted to maintain a tort cause of action for emotional distress. Molien further establishes that a plaintiff who has suffered serious emotional distress, as a result of the defendant’s breach of duty to him or her, is entitled to recover for such distress even when the distress itself has not resulted in any physical manifestation of injury.