Watching porn culminates either in masturbation or intercourse. Whatever physiological or hormonal changes that do take place during the act of watching porn get "nullified" at/after orgasm. Hence the physical changes in the body, as I see them, are temporary.
This is true for men as well as women watching porn.

The prime reason for watching porn in the first place is not physical but psychological. We crave sexual stimulation in our minds, and once the tension is released, the mind's disturbance also subsides. However, unlike the body's physical changes, which are restored to the pre-porn initial state, the effect on the mind is cumulative. Some of that craving is retained even after tensions are released, and this has a positive feedback effect. The mind craves for more, and more, and more; and puts the body through repeated "stress cycles" if I may put it that way.

In extreme cases, which are not too rare, there comes a limit to what the body can take, and then it retaliates in the one way it knows best: it simply switches off. Once this happens, the stimulation fails to take effect ... and Viagra (or its female equivalent) would enter into one's life.

Stimulation of the senses is an ancient story. The methods employed today are of modern nature but the same were used in ancient times also.Take the case of courtesans in the ancient kingdoms,harems,baths,stimulan ts,etc etc..the list is endless. Some of the most brilliant architectures in the Hindu temples depicts forms in various stimulating poses too, that itself would amount to pornography if viewed from senses perspective!The delusion of the senses takes place by such methods and the physical arousal also happens.These are body changes to the surrounding situations which are healthy but excesses in any form may not be conducive to that human being.These are methods employed for human progression in moderation only. Any such acts in excess are habit forming which may be hard to break.+