High entropy alloys (HEAs) are promising nuclear structural materials due to their excellent irradiation resistance. However, the essential mechanisms of irradiation tolerance in HEAs remain largely inferential and imperfectly understood. This study investigates the evolution of irradiation-induced nano-scale microstructures in Ni, FeNiCr, FeNiCrCoCu and FeNiCrCuAl HEA models by molecular dynamics simulations to elucidate the conundrums. As fewer irradiation-induced Frenkel pair (FP) residuals were found in the FeNiCrCuAl HEA model in comparison with other models, a high resistance of the HEAs to the generation of permanent defects was indicated, while also the associated relatively long thermal spike and slow recrystallization stimulated a high efficiency for the recombination/annihilation of FPs to underscore a superior structural recovery of the HEAs. Under the influence of compositional increases of constituent elements, the effect of severe lattice distortion by energetics modifications was found to stimulate decreased atomic mobility accompanied by inhibited dislocation formation. The evolution of the models' lattices in terms of their capacity to restrict interstitials and repair defects revealed that the self-healing/recovery mechanism that confirmed the highest initial lattice distortion value accompanied by the least lattice re-distortion value in the FeNiCrCuAl HEA model is key to the observed superior irradiation tolerance of the HEA models. Thus, by feasibly enhancing lattice distortion in crystalline materials, notably in HEAs, promising and potentially high irradiation-resistant structural materials can be developed.