OPINION
MOTZ, Circuit Judge:
Ghulam Nasim appeals from the district court’s dismissal of his complaint against the Warden of the Maryland House of Correction and certain other prison officials as untimely. Because it is not apparent from the face of Nasim’s complaint that it was not filed within the prescribed statute of limitations period, we reverse.
I.
Proceeding pro se, Nasim filed a complaint and application to proceed informa pauperis in the District of Maryland on September 17, 1993, alleging violations of 42 U.S.C. §§ 1983 and 1985. The complaint alleged that Nasim was confined at the Maryland House of Correction in Jessup, Maryland, from April, 1983 until November 15, 1989, during which time he was denied “needed treatment for stroke and spinal disk disease” and “suffered several attacks of relapse from stroke, lung disease, eye disease and skin lesions” because of asbestos exposure. The complaint further alleged that “[i]n first half of 1988 and second half of 1989” Nasim observed asbestos “fall[1474]*1474ing from ceiling into [his] cage,” that there was “no notice, information nor a wa[r]ning” as to the asbestos, and that, despite Nasim’s complaints to “doctors, nurses and warden,” prison officials failed to take any measures to “protect plaintiff and other inmates.” Finally, the complaint alleged that Nasim “suffered permanent medical and psychological injuries by forcing to inhale cancer causing asbestos chemicals, maliciously and secretly dumped upon plaintiff during 1988-1989, without any warning or protection to the helpless prisoner in cage....” (all errors in original).
On October 5, 1993, without directing service upon the defendants, the district court granted Nasim leave to proceed in forma pauperis but then dismissed his complaint with prejudice as untimely.1 Nasim filed a motion for reconsideration, in which he asserted that it was not until 1991, after reading relevant news articles and securing certain information under the Freedom of Information Act, that he realized that the asbestos was the probable cause of his injuries. The district court denied Nasim’s motion for reconsideration, again without directing service and before receipt of any pleading from the defendants, and this appeal followed.
II.
The district court dismissed Nasim’s complaint pursuant to 28 U.S.C. § 1915(d), which “allows the courts to dismiss an in forma pauperis complaint ‘if satisfied that the action is frivolous or malicious.’ ” Denton v. Hernandez, — U.S. -, -, 112 S.Ct. 1728, 1733, 118 L.Ed.2d 340 (1992) (quoting 28 U.S.C. § 1915(d)). “[A] complaint, containing as it does both factual allegations and legal conclusions, is frivolous where it lacks an arguable basis either in law or in fact.” Neitzke v. Williams, 490 U.S. 319, 325, 109 S.Ct. 1827, 1831-32, 104 L.Ed.2d 338 (1989). A district court’s determination that a claim is “frivolous” is reviewed for abuse of discretion. Denton, — U.S. at -, 112 S.Ct. at 1734; see also White v. Gregory, 1 F.3d 267, 269 (4th Cir.1993); Brown v. Briscoe, 998 F.2d 201, 203 (4th Cir.1993) (per curiam). As we recently explained in Adams v. Rice, “it would defeat the purpose of § 1915(d),” i.e., the prevention of “abuse of the judicial system by parties who. bear none of the ordinary financial disincentives to filing meritless claims,” to review § 1915 dismissals “without substantial deference to the district courts.” Adams v. Rice, 40 F.3d 72, 74 (4th Cir.1994).
Of course, this does not mean that a district court’s discretion to grant a § 1915(d) dismissal is unbridled, or that such discretion is not subject to appellate review. A complaint is properly dismissed pursuant to § 1915(d) as factually frivolous only if its factual allegations are “fantastic,” “delusional,” or otherwise “clearly baseless,” and as legally frivolous only if its claims are based on an “indisputably meritless legal theory.” Neitzke, 490 U.S. at 327, 109 S.Ct. at 1833. Accordingly, the task of an appellate court in reviewing a § 1915(d) dismissal on one, or both, of these grounds is to determine whether these standards were met.
This is illustrated by our recent analysis in Adams. There, the plaintiff, a prisoner who had been assigned to “single-cell housing,” alleged that prison officials “retaliated” against him by (1) refusing to transfer him to protective custody, (2) denying him minimum custody status, (3) failing to schedule a parole eligibility date and hearing, and (4) barring his access to the grievance process. Adams, 40 F.3d at 75. The district court found that Adams’ factual claims were “clearly baseless” and that his legal theory “lacked an arguable basis in law.” Id. at 74. After [1475]*1475noting the peculiar nature of such “retaliation” claims by prisoners, ie., “[e]very act of. discipline by prison officials is by definition ‘retaliatory’ in the sense that it responds directly to prisoner misconduct” and “must therefore be regarded with skepticism, lest federal courts embroil themselves in every disciplinary act that occurs in state penal institutions,” id. at 74, we addressed separately each basis for the § 1915(d) dismissal. Because the “nonsensical” ■ complaint in Adams “fail[ed] to allege how or why defendants retaliated against plaintiff,” or why his single-cell housing “was inferior to or even different from protective custody,” we concluded that the district court had not abused its discretion in finding that the complaint “was clearly baseless in fact.” Id. at 74-75. Moreover, because the “retaliation” claim failed to implicate any constitutional right, we concluded that the district court had not abused its discretion in finding that the complaint “‘lack[ed] even an arguable basis in law.’ ” Id. at 75 (quoting Neitzke, 490 U.S. at 328, 109 S.Ct. at 1833).
The analysis employed in Adams is precisely what is required when an appellate court must determine whether a district judge abused his discretion in dismissing a complaint pursuant to § 1915(d) because its factual allegations were “clearly baseless” or because it was based on an “indisputably meritless legal theory.” Neither of these grounds, however, provides the basis for dismissal here; nor could they. Comparison between this case and Adams is instructive. First, Nasim’s claim, unlike that in Adams, is not that prison officials “retaliated” against him,2 but that they exposed him to a toxic substance — asbestos—that endangered his health. Moreover, the complaint here, again unlike that in Adams, contains specific allegations as to “how and why” defendants assertedly violated the plaintiffs rights, ie., by permitting asbestos to “fall[ ] from ceiling into the Plaintiffs cage” in 1988' and 1989 without “notice, information ... wa[r]ning or protection provided to the Plaintiff.” Although the factual allegations here are unlikely,3 they are not “nonsensical.” Compare Adams, 40 F.3d at 75. Furthermore, a claim that prison officials have purposely or with deliberate indifference exposed a prisoner to a toxic substance, unlike the claim of retaliation in Adams, does have a constitutional basis, ie., the Eighth Amendment. See Hell-ing v. McKinney, — U.S. -, -, 113 S.Ct. 2475, 2481-82, 125 L.Ed.2d 22 (1993) (prisoner states “a cause of action under the Eighth Amendment” when alleging prison officials, “with deliberate indifference, exposed him” to toxic substance).
Thus, Nasim’s complaint, unlike that in Adams, does not contain factual allegations that are on their face “nonsensical,” “clearly baseless,” or wholly conelusory. Nor does the complaint here, again unlike that in Adams, lack “even an arguable basis in law.” Rather, Nasim’s legal theory — that prison officials deliberately exposed him to toxic substances — has been specifically recognized by the Supreme Court as stating a cause of action under, the Eighth Amendment. See Helling, — U.S. at-, 113 S.Ct. at 2481. Moreover, as noted above, the district court did not hold to the contrary. Unlike the district court in Adams, the court here did not dismiss the complaint because the factual allegations were “clearly baseless” or because the legal theory was without “an arguable basis in law.” Rather, the district court dismissed Nasim’s complaint solely because it concluded that the complaint “ha[d] been filed outside the statute of limitations.” In sum, the complaint was dismissed, not because of some defect in the complaint itself, but because the court found there was a [1476]*1476meritorious affirmative defense to the allegations in the1 complaint.
At one time it was unclear whether, pursuant to § 1915(d), a district court could dismiss a complaint on the basis of a waivable affirmative defense,4 before receiving any responsive pleading asserting this defense. See Anger v. Revco Drug Co., 791 F.2d 956, 958 (D.C.Cir.1986) (sua sponte § 1915(d) dismissal because of lack of personal jurisdiction over defendants held improper); Sinwell v. Shapp, 536 F.2d 15, 19 (3d Cir.1976) (sua sponte § 1915(d) dismissal because of improper venue held improper). This Court, however, led the way in concluding that under certain circumstances such a dismissal was proper. See Todd v. Baskerville, 712 F.2d 70 (4th Cir.1983), aff'g sub nom. Holsey v. Bass, 519 F.Supp. 395 (D.Md.1981).
In Holsey, the district court properly acknowledged that “[generally, it is the duty of the defendant to plead affirmative defenses, and the court cannot raise such defenses sua sponte,” but concluded “that given the competing policy considerations reflected in § 1915(d) ... such defenses should be considered by a court sua sponte, in certain limited circumstances....” Holsey, 519 F.Supp. at 408-09 (citing, Fed.R.Civ.P. 8(c)). On appeal, we specifically noted that the district court had “recognized that there was some dispute in the authorities on the power of the Court to consider affirmative defenses in ruling on dismissal for frivolousness under § 1915(d) but concluded that such defenses could be considered ‘in certain limited circumstances, such as those found in the case at bar.’” Todd, 712 F.2d at 74 (quoting Holsey, 519 F.Supp. at 409). Those “certain limited circumstances” were, we noted, a “specific” finding by the district court that the plaintiffs claims “were manifestly barred because it appeared on the face of the eom-plaint and the court records that ... [principles of collateral estoppel and] the applicable statute of limitations bar[ ] ... the acts of which plaintiff complains.” Id. As Judge Russell explained, “[ujnder those facts, we agree with the conclusions of the District Court and accordingly affirm the judgment of dismissal entered by it herein.” Id, (emphasis added).
This Court has not had an occasion, other than Todd, to discuss in a published opinion a district court’s sua sponte § 1915(d) dismissal on affirmative defense grounds.5 The conclusion reached in Todd, however, has in recent years been adopted by a number of other courts. For example, in Yellen v. Cooper, 828 F.2d 1471 (10th Cir.1987), the Tenth Circuit, relying on Todd, affirmed a sua sponte § 1915(d) dismissal on waiver grounds. In doing so, the Yellen court carefully explained why such a dismissal does not violate the policy underlying Fed.R.Civ.P. 8(c):
[T]he policy underlying Rule 8(e), affording the plaintiff adequate notice of unanticipated defenses, is not violated when the plaintiff’s in forma pauperis complaint itself sets out facts plainly demonstrating the affirmative defense.
Id. at 1476 (emphasis added).6
Cognizant of the competing policy considerations inherent in § 1915(d) and Rule 8(c), in recent years every federal appellate court to address the question appears to have similarly concluded that even if a complaint is neither factually nor legally baseless, a sua sponte § 1915(d) dismissal can be justified if “it is clear from the face of a complaint filed in forma pauperis that the claims asserted are barred by the applicable statute of limitations -” Gartrell v. Gaylor, 981 F.2d 254, 256 (5th Cir.1993). Accordingly, our sister circuits have affirmed sua sponte § 1915(d) [1477]*1477dismissals on limitations grounds, but only when it was clear from the face of the complaint that limitations barred the claims. See, e.g., Moore v. McDonald, 30 F.3d 616, 620 (5th Cir.1994) (affirming dismissal); Slack v. Carpenter, 7 F.3d 418, 419-20 (5th Cir.1993) (same); Niccolai v. U.S. Bureau of Prisons, 4 F.3d 691, 692-93 (8th Cir.1993) (reversing dismissal); Gartrell v. Gaylor, 981 F.2d at 256-59 (same); Johnson v. Rodriguez, 943 F.2d 104, 107-108 (1st Cir.1991) (affirming dismissal), cert. denied, — U.S. -, 112 S.Ct. 948, 117 L.Ed.2d 117 (1992); Street v. Vose, 936 F.2d 38, 39 (1st Cir.1991) (same), cert. denied, — U.S. -, 112 S.Ct. 948, 117 L.Ed.2d 117 (1992); see also Yellen, 828 F.2d at 1476 (affirming dismissal when the “complaint on its face” demonstrated waiver); Clark v. Georgia Pardons & Paroles Bd., 915 F.2d 636, 640 (11th Cir.1990) (dicta). See generally Brownlee v. Conine, 957 F.2d 353 (7th Cir.1992) (Posner, J.).
Thus, prior to the filing of any defensive pleading asserting limitations, a district court only has discretion to grant a § 1915(d) dismissal on that ground when the limitations bar is clear from the face of the complaint. See, e.g., Moore, 30 F.3d at 620; Slack, 7 F.3d at 419; Gartrell, 981 F.2d at 256; Yellen, 828 F.2d at 1476.7 For this reason, appropriate review of such § 1915(d) dismissals requires appellate courts to examine carefully both the complaint and the legal principles governing the limitations defense. See, e.g., Gartrell, 981 F.2d at 256-59; Street, 936 F.2d at 39-41. It is to that examination that we now turn.
III.
The parties agree that the relevant statute of limitations is Maryland’s, general three-year statute of limitations for civil actions, see Wilson v. Garcia, 471 U.S. 261, 266-67, 105 S.Ct. 1938, 1941-42, 85 L.Ed.2d 254 (1985). They also agree that this cause of action accrues when the plaintiff “knows or has reason to know of the injury which is the basis of the action.” See Cox v. Stanton, 529 F.2d 47, 50 (4th Cir.1975) (although “[t]he time limitation for civil rights actions, such as those under § 1983, is borrowed from state law ... [t]he time of accrual of a civil rights action is a question of federal law”).
A medical condition need not be diagnosed as such for an action on that condition to accrue, nor need a plaintiff fully understand the legal consequences of his or her condition. United States v. Kubrick, 444 U.S. 111, 122-24, 100 S.Ct. 352, 359-60, 62 L.Ed.2d 259 (1979). Instead, a plaintiff need only be “aware of his injury and its probable cause.” Id. at 118, 100 S.Ct. at 357; see also Muth v. United States, 1 F.3d 246, 249 (4th Cir.1993); Childers Oil Co. v. Exxon Corp., 960 F.2d 1265, 1272 (4th Cir.1992) (“The ‘discovery rule’ tolls a statute of limitations until the plaintiff has, or ought to have, answers to two questions: Am I injured? Who injured me? At that point, the plaintiff has enough information to begin investigating his claims”) (citing Kubrick, 444 U.S. at 122, 100 S.Ct. at 359); Gould v. United States Dep’t of Health and Human Servs., 905 F.2d 738, 742 [1478]*1478(4th Cir.1990) (en banc), cert. denied, 498 U.S. 1025, 111 S.Ct. 673, 112 L.Ed.2d 666 (1991); Blanch v. McKeen, 707 F.2d 817, 819 (4th Cir.) (cause'of action does not accrue until plaintiff exercising due diligence should have discovered factual basis for claim), cert. denied, 464 U.S. 916, 104 S.Ct. 279, 78 L.Ed.2d 258 (1983).
The district court understood that in order for Nasim’s causé of action to have accrued, Nasim must have been aware of his injuries. However, it is unclear whether the court further understood' that in order for the cause of action to have accrued, Nasim must also have been aware of the probable cause of those injuries. The court found that Na-sim “at the latest, should have known of his injury when he personally observed the asbestos being removed in 1989” (emphasis added). The court did not make any finding as to when Nasim knew or should have known of the probable 'cause of his injuries. Thus, there is no finding by the district court that the complaint was not filed within three years from the date on which Nasim’s claims accrued, i.e., within three years from the date on which he knew or should have known of the probable cause of his injury.
Nor is this clear from the face of the complaint. Of course, nowhere in his complaint did Nasim state when he became aware of the causal connection between asbestos and his injuries. He does allege that from 1983 to 1989 he was denied treatment for “stroke and spinal disk disease” and “suffered several attacks of relapse from stroke, lung disease, eye disease and skin lesions from asbestos exposure_” He further alleges that in the “first half of. 1988 and second half of 1989,” without “notice, information ... wa[r]ning or protection,” asbestos fell “from ceiling into [his] cage,” that he reported this to “doctors, nurses and warden” but nothing was done to protect him or the other prisoners, and that he “suffered permanent medical and psychological injuries” because he was forced “to inhale cancer causing asbestos chemicals, maliciously and secretly dumped upon [him] during 1988-1989, without any warning or protection....”
Thus, the complaint makes clear that by 1989, Nasim knew (1), he had been exposed to asbestos, (2) asbestos exposure posed a health risk, and (3) he was suffering from various health problems. To conclude from these bare facts, derived from his pro se complaint, that contemporaneously Nasim knew or should have known that the asbestos was also the probable cause of his health problems, or that he somehow failed to exercise the requisite due diligence in discovering the cause of those problems, assumes too much.8
Indeed, according to his complaint Nasim was in bad health prior to 1988, requiring treatment and medication for a stroke and “spinal disk disease.” Thus, it would not have been unreasonable for Nasim initially to fail to recognize asbestos as the probable cause of his 1989 health problems. This is particularly true in view of the fact that asbestos injuries are typically latent in nature, not manifesting themselves until several years after exposure. See Taurel v. Central Gulf Lines, Inc., 947 F.2d 769, 771 (5th Cir.1991). In his motion for reconsideration, filed shortly after the complaint was dismissed, Nasim asserted that in 1989 he had “no knowledge whatsoever that asbestos chemicals caused cancer and cardio-vaseular disease, like stroke or heart ailments” but instead “all the blame was laid on denial of medical treatment and conspiracy latter discovered from prison hospital files in 1987” (emphasis in original). It was assertedly not until receiving information pursuant to an October, 1991 Freedom of Information Act [1479]*1479request and reviewing newspaper articles on the “adverse effects of exposure to asbestos” that Nasim had reason to know that “exposure to cancer-causing asbestos chemicals had enhanced plaintiffs relapse from stroke_” Of course, all of these assertions may ultimately prove to be false, but there is certainly nothing on the face of the complaint demonstrating as much. Because there is no indication on the face of the complaint as to when Nasim knew or should have known that asbestos was the probable cause óf his injuries, his complaint should not have been sua sponte dismissed pursuant to § 1915(d) as untimely.9
The case law supports this conclusion. In Portis v. United States, 483 F.2d 670 (4th Cir.1973), the plaintiff was treated in October, 1963 with neomycin and immediately suffered from severe renal toxicity. Because hearing loss is a possible side effect from the intramuscular administration of neomycin, the plaintiffs hearing was cheeked before she was discharged from the hospital, and although no damage was then evident, she was advised to have her hearing checked periodically thereafter. The plaintiffs hearing deteriorated, but none of the physicians who examined her diagnosed the cause of hearing loss. It was not until 1969 that a doctor finally diagnosed the plaintiffs problem as related to neomycin toxicity. The plaintiff brought suit in 1970, and this Court held that her claim had not accrued until 1969. The Court stated that “[e]ven if [the plaintiff] knew that there was a ‘distinct possibility’ of a causal relationship, ... [w]hat is important here is that no one, neither layman nor doctor, diagnosed the hearing difficulty as being caused, or even probably caused, by the 1963 malpractice until the year 1969.” Id. at 673;10 see also Childers Oil Co., 960 F.2d at 1272; Townley, 887 F.2d at 501.
In Kubrick, on the other hand, the Supreme Court held that the statute of limitations had run and that the plaintiffs complaint was therefore untimely. There, the plaintiff was treated for an infection with neomycin in 1968, and six weeks later he experienced a ringing sensation in his ears and some loss of hearing. In January, 1969, a physician informed the plaintiff that it was “highly possible” that his hearing loss was caused by the neomycin. In June, 1971, the plaintiff was told by another physician that the neomycin in fact caused his injury and should not have been administered. The plaintiff filed suit in 1972. The lower courts held that “even though a plaintiff is aware of his injury and of the defendant’s responsibility for it, the statute of limitations does not run where the plaintiff shows that ‘in the exercise of due diligence he did not know, nor should he have known, facts which would have alerted a reasonable person to the possibility that the treatment was improper.’ ” Kubrick, 444 U.S. at' 116, 100 S.Ct. at 356 (quoting 581 F.2d 1092, 1097 (3d Cir.1978)) (emphasis added). The Supreme Court reversed, holding that, because the plaintiff was aware in 1969 that he had been injured and that the defendant’s actions were the “probable cause” of his injury, his cause of action had accrued at that time, even if the [1480]*1480plaintiff was then unaware of the legal implications of the defendant’s actions, i.e., that those actions constituted medical malpractice. Id. at 122-24, 100 S.Ct. at 359-60. In so holding, the Court emphasized that the plaintiff “had been in possession of all the facts about the cause of his injury since January 1969.” Id. at 123, 100 S.Ct. at 360. Here, in contrast, although Nasim was aware as early as 1989 that he had health problems and that he had been exposed to asbestos, he assertedly was not aware until 1991 that asbestos had “caused” his stroke “relapse” or “cancer and cardio-vascular disease.”
Indeed, there is nothing in Nasim’s complaint indicating when he knew that asbestos was the probable, or even the possible, cause of his various health problems. It was not until after the complaint was dismissed, when Nasim filed his motion for reconsideration, that the date on which he allegedly discovered that asbestos was the probable cause of his injuries — October, 1991 — became apparent. A general awareness that asbestos poses certain unidentified health risks, as evidenced here by Nasim’s complaints to prison officials, does not warrant the conclusion, at least at this preliminary stage, that Nasim “possessed sufficient information that he knew, or should have known,” Townley, 887 F.2d at 501, that the asbestos was the probable cause of his health problems, or even that 'he had been “put on a duty to inquire,” Childers Oil Co., 960 F.2d at 1272, about the cause of those problems, particularly in view of the fact that many of his health problems predated his exposure to asbestos. Indeed, given the convoluted nature of Nasim’s complaint, any conclusions drawn from it about what he knew or should have known in 1988 and 1989, or about his efforts to discover the cause of his injuries, would be pure speculation, and a proper determination of the timeliness of Nasim’s complaint requires a more fully developed record.11
Finally, we note that in the only case that we have found in which a similar fact situation has arisen in the context of a sua sponte § 1915(d) dismissal, the Fifth Circuit reached the same conclusion. See Phillips v. Purdy, 617 F.2d 139 (5th Cir.1980). There, a prisoner filed a pro se complaint alleging that he had “contracted tuberculosis while confined in the [Dade County] jail because of inadequate treatment for his illness and improper and unsanitary jail conditions.” Id. at 140. The district court sua sponte dismissed the complaint pursuant to § 1915(d), finding it was barred by the relevant four-year limitations period because the prisoner had been transferred out of the Dade County Jail in November, 1973, more than four years prior to filing suit in December, 1978. Id. The prisoner asserted that he did not discover until 1976 the causal connection between conditions at the Dade County Jail and his contracting tuberculosis. Id. The Fifth Circuit reversed, reasoning:
We are unable to determine from the state of the record, since the case was dismissed without an evidentiary hearing, if the allegations in the complaint are true. Dismissal was improper under the circumstances. If the plaintiff is able to show a satisfactory reason why he did not learn until 1976 that his tuberculosis condition was brought about by his confinement in the Dade County Jail, the period of limitations may not have begun to run until that time.:.. We are likewise unable to decide without the benefit of the record of an evidentiary hearing that suit was properly dismissed under 28 U.S.C. § 1915(d) pertaining to frivolous or malicious actions.
Id. at 140-41 (citations omitted).
The same rationale requires reversal here. The district court abused its discretion in sua sponte dismissing Nasim’s complaint pursuant to § 1915(d).
REVERSED.