This is an appeal from an April 4, 1995, decision of the Board of Veterans’ Appeals (BVA or Board) which determined that new and material evidence had not been submitted to reopen the appellant’s claim for service connection for psoriasis. The appellant filed a motion to remand, or for acceptance of the motion in lieu of a brief, and for a stay of proceedings. The Secretary filed a response contesting the grounds upon which the appellant proposes a remand, but requesting a remand on a separate ground. This appeal is timely and the Court has jurisdiction pursuant to 38 U.S.C. § 7252(a). For the reasons that follow, the Court will deny the motions for remand, accept the motions in lieu of briefs, and affirm the Board’s decision.
I.
The appellant served on active duty in the U.S. Navy from December 1977 to October 1978. Record (R.) at 56. He had attempted to join in April 1977 but was disqualified for service due to psoriasis on both legs. R. at 19-20. In July 1977, the appellant’s private physician wrote a letter stating that he had been treating the appellant for the rash on his legs and believed it to be an “eczematous patch ... with some secondary infection.” R. at 23. His service entrance examination was changed to read “eczema, only episod[ic], now clear.” R. at 20.
While in service, the appellant was treated for scaling on the knees, elbows, and palms (see R. at 19-54) and was subsequently diagnosed with psoriasis (R. at 34). He continued to suffer from psoriasis throughout service, though it improved slightly. Finally, in September 1978, a navy physician recommended discharge, noting that the appellant’s psoriasis was not aggravated in service. R. at 44. A September 1978 report by the medical board rendered a final diagnosis of psoriasis vulgaris and found that the condition had existed prior to service and was not aggravated in service. R. at 50. The report noted that the appellant had stated that he had developed this problem approximately two years prior to enlistment in the Navy. R. at 49. The appellant was subsequently discharged.
In January 1979, the appellant filed a claim for service connection for psoriasis. R. at 58. Later that month, the VA regional office (RO) issued a rating decision denying the appellant’s claim. The RO noted that the appellant’s condition was neither “incurred in nor aggravated by his short period of active duty.” R. at 61. The RO found that psoriasis was noted on the entrance examination and that the appellant had a history of treatment prior to service and shortly after entry into service. Ibid. The RO’s decision was confirmed in July 1979 and became final.
The appellant sought to reopen his claim in May 1988, and was advised to submit new and material evidence related to the issue of aggravation in service. In September 1992, the appellant submitted medical records in support of his claim. R. at 87-126. The post-service medical records showed diagnoses of and treatment for psoriasis, which often was quite severe. In December 1992, the RO confirmed its previous rating decision after finding that the newly submitted medi*186cal records did not show that the appellant’s psoriasis was incurred in or aggravated by service. R. at 130.
In May 1993, the appellant filed an appeal with the BVA. R. at 149. The Board found that the “[e]vidence received since the January 1979 unappealed rating decision is not new and material to reopen the [appellant’s] claim [for] service connection for psoriasis.” The appellant thereafter appealed to this Court.
II.
The Secretary shall reopen a previously disallowed claim upon the presentation by the claimant of new and material evidence. 38 U.S.C. § 5108. The issue of whether evidence is new and material is a conclusion of law which the Court reviews de novo. Beausoleil v. Brown, 8 Vet.App. 459, 463 (1996). The Secretary must perform a two-step analysis when a veteran seeks to reopen a final decision based on new and material evidence. Manio v. Derwinski, 1 Vet.App. 140, 145 (1991). First, it must determine whether the evidence presented or secured since the last final disallowance is “new and material.” Ibid; see also Edenfield v. Brown, 8 Vet.App. 384, 389-90 (1995) (en banc) (holding that a denial on the merits and a determination that a claim is not well grounded both constitute a “disallowance” of a claim). If it is, the Board must then reopen the claim and review the new evidence “in the context of’ the old to determine whether the prior disposition of the claim should be altered. Manio, 1 Vet.App. at 145; Jones v. Derwinski, 1 Vet.App. 210, 215 (1991).
In Evans v. Brown, 9 Vet.App. 273, 283 (1996), this Court stated that step one of the Manió two-step process, the determination of whether the evidence is new and material, involves three questions. The first question is whether the newly presented evidence is actually “new” in the sense that it was not of record at the time of the last final disallowance of the claim and is not merely cumulative of other evidence of record. Ibid.; Struck v. Brown, 9 Vet.App. 145, 151 (1996). The second question is whether the evidence is “probative” of the “issue at hand.” Evans, 9 Vet.App. at 283. Evidence is “probative” when it “tend[s] to prove, or actually prov[es] an issue.” Black’s Law Dictionary 1203 (6th ed. 1990). The third question is whether, in light of all of the evidence of record, there is a reasonable possibility that the outcome of the claim on the merits would be changed. Dolan v. Brown, 9 Vet.App. 358, 361 (1996); Evans, 9 Vet.App. at 283. Affirmative answers to both materiality questions are required in order for “new” evidence to be “material.” Ibid.; Blackburn v. Brown, 8 Vet.App. 97, 102 (1995). As to those two “materiality” components, the evidence is presumed credible for the purpose of determining whether the case should be reopened. Justus v. Principi, 3 Vet.App. 510, 513 (1992).
The issue in this ease is whether the appellant’s condition began during service or was aggravated by service. The evidence submitted since the last final disallowance in 1979 includes post-service medical records and the appellant’s own statements. While the medical records show post-service diagnoses of psoriasis, often severe, none of this evidence relates the appellant’s condition to his service. In addition, the medical reports show that none of the treating physicians opined that the psoriasis had worsened during service. As a result, this newly submitted evidence is not probative of the issue at hand and therefore does not constitute new and material evidence. See Evans, supra.
The appellant’s own statements that his condition worsened in service are also not probative of the issue at hand. Lay assertions of medical causation, or in this case, of aggravation of a preexisting disease, cannot suffice to reopen a claim under 38 U.S.C. § 5108. Wilkinson v. Brown, 8 Vet.App. 263, 268 (1995); see also Moray v. Brown, 5 Vet.App. 211, 214 (1993). While the appellant is certainly capable of providing evidence of symptomatology, a layperson is generally not capable of opining on matters requiring medical knowledge, such as the condition causing or aggravating the symptoms. See Stadin v. Brown, 8 Vet.App. 280, 284 (1995); Robinette v. Brown, 8 Vet.App. 69, 74 (1995).
*187The appellant also contends that the Board erred by not addressing the presumption of soundness under 38 C.F.R. § 3.304(b) and the presumption of aggravation of a preexisting disease under 38 C.F.R. § 3.306. However, the Board was not required to reach these issues unless the claim was reopened. Cf. Annoni v. Brown, 5 Vet.App. 463, 467 (1993) (where Court held that benefit of the doubt doctrine does not apply when appellant fails to fulfill threshold burden of submitting new and material evidence); Gilbert v. Derwinski, 1 Vet.App. 49, 55 (1990). Since the Court finds that the appellant has not submitted new and material evidence to reopen his claim, these issues will not be addressed here.
III.
In his response the Secretary argues that the BVA decision should be summarily affirmed. Appellee’s Response at 7. However, in that same pleading, the Secretary also moves for a remand of the claim to allow de novo review by the BVA in light of a 1992 change in 38 C.F.R. § 3.306(b). The regulation was changed to establish, in certain circumstances, a presumption of aggravation which can only be rebutted by clear and unmistakable evidence. The Secretary, citing Spencer v. Brown, 4 Vet.App. 283 (1993), contends that this change in the regulation may give rise to a new entitlement, thus requiring its application to the appellant’s claim. However, while it does appear that a change in a law or regulation can constitute new and material evidence under appropriate circumstances, see Jensen v. Brown, 19 F.3d 1413 (Fed.Cir.), on remand, 7 Vet.App. 27, 28 (1994), the record before the Court compels the conclusion that this appeal does not present such circumstances.
Section 3.306(a) of Title 38, Code of Federal Regulations, provides:
A preexisting injury or disease will be considered to have been aggravated by active military, naval, or air service, where there is an increase in disability during such service, unless there is a specific finding that the increase in disability is due to the natural progression of the disease.
(Emphasis added). In Falzone v. Brown, the Court held that the presumption of aggravation created by 38 C.F.R. § 3.306 applies only if there is an increase in severity during service. 8 Vet.App. 398, 402 (1995). The Board found as a matter of fact that the newly submitted records “do not show that there was an increase in the severity of [the appellant’s] psoriasis” during service. R. at 6. There is a plausible basis in the record for the Board’s finding of fact. See Gilbert, 1 Vet.App. at 53 (Court cannot overturn factual determinations of the BVA if there is a plausible basis in the record for such determinations). Therefore, the regulation is not applicable to the appellant’s claim and the Secretary’s motion to remand the claim to the BVA for de novo review in light of the change in 38 C.F.R. § 3.306 will be denied.
IV.
Upon consideration of the record, the appellant’s motion for remand accepted by the Court in lieu of a brief, and the Secretary’s response, also accepted in lieu of a brief, the Court holds that the appellant has not demonstrated that the Board committed either factual or legal error which would warrant reversal or remand. Gilbert, supra; see also Anderson v. City of Bessemer City, 470 U.S. 564, 105 S.Ct. 1504, 84 L.Ed.2d 518 (1985); Danville Plywood Corp. v. United States, 899 F.2d 3 (Fed.Cir.1990). The Court also is satisfied that the BVA decision meets the “reasons or bases” requirements of 38 U.S.C. § 7104(d)(1), and the benefit of the doubt doctrine of 38 U.S.C. § 5107(b). See Gilbert, supra. Accordingly, the appellant’s motion for remand is denied, the Secretary’s motion for remand on other grounds is denied, and the April 4, 1995, decision of the Board of Veterans’ Appeals is AFFIRMED.