This is a good question but happily, having hypnosis isn't like getting a tan that fades in time!
Really hypnosis is about learning new things. But it doesn't feel like learning because it happens on an unconscious level.
Rather than worrying about whether hypnotic benefits will wear off. I could ask you:
"How many unexpected 'ripple effect' benefits might you notice as a result of this one area of your life improving?"
Hypnosis can seem miraculous and people are often amazed that a life long phobia or smoking habit can be cured in such a relatively short space of time.
But another way of looking at it is that phobias, fears and compulsive behaviours are often learned by the brain very fast in the first place which means that, of course, the brain has the power to unlearn them fast too. And hypnosis is the perfect way to do that.
So a brief experience - whether traumatic or therapeutic - can have a lasting effect.
Once you have overcome a phobia, or blushing, or shyness, then the experiences you have, once things have improved, help 'glue' these changes into place even more strongly.
Plus - once you've bought your hypnosis session you have it forever, so you can listen to it whenever you like in the future.