Thomas Aquinas, Compendium of Theology

Although the bodies of the damned will be capable of suffering, they will not be subject to corruption. This is a fact we have to admit, even though it may seem to disagree with present experience, according to which heightened suffering tends to deteriorate substance. In spite of this, there are two reasons why suffering that lasts forever will not corrupt the bodies undergoing it.

First, when the movement of the heavens ceases, as we said above, all transformation of nature must come to a stop. Nothing will be capable of alteration in its nature; only the soul will be able to admit some alteration. In speaking of an alteration of nature, I mean, for instance, a change from hot to cold in a thing, or any other such variation in the line of natural qualities. And by alteration of the soul I mean the modification that takes place when a thing receives a quality, not according to the quality's natural mode of being, but according to its own spiritual mode of being; for example, the pupil of the eye receives the form of a color, not that it may be colored itself, but that it may perceive color. In this way the bodies of the damned will suffer from fire or from some other material agent, not that they may be transformed into the likeness or quality of fire, but that they may experience the effects characteristic of its qualities. And this experience will be painful, because the effects produced by the action of fire are opposed to the harmony in which the pleasure of sense consists. Yet the action of hell-fire will not cause corruption, because spiritual reception of forms does not modify bodily nature, except, it may be, indirectly.

The second reason is drawn from a consideration of the soul, in whose perpetual duration the body will be forced, by divine power, to share. The condemned person's soul, so far as it is the form and nature of such a body, will confer never-ending existence on the latter. But because of its imperfection, the soul will not be able to bestow on the body immunity from suffering. Consequently the bodies of the damned will suffer forever, but will not undergo dissolution.