How Water Vapour Therapy Shrinks the Prostate — and What the Shrinkage Does Not Tell You

Last updated: August 25, 2026

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Men ask this constantly, and it is a fair question: if nothing is cut out, how does the prostate get smaller? The answer is a piece of physics, and understanding it also explains why the improvement takes months rather than days.

• Urology center Bangkok hospital Thailand Booking online 02-310-3009 bhquro@bdms.co.th
• Samitivej Sriracha hospital Chonburi 088-022-1445

Related reading: what benign prostatic enlargement actually is · Rezum: what it does and what to expect · patient instructions after the procedure

Why an enlarged prostate causes trouble

Benign enlargement is usual in men over fifty, and where it obstructs the channel it produces a weak stream, hesitancy, getting up at night and a sense of not emptying. Medication helps many men. It is also the reason many men look for something else — alpha blockers commonly cause dizziness on standing and a change in ejaculation, and 5-alpha reductase inhibitors can affect libido and erections.

An earlier version of this article described erectile dysfunction as the big problem with prostate medication generally. That is too broad: the dominant complaints with alpha blockers are dizziness and ejaculatory change rather than erectile failure, and the two drug classes differ from each other. The point stands that side effects drive men to look for alternatives — it is simply not one uniform side effect.

The physics: why steam and not simply heat

Other minimally invasive treatments conduct heat outward from a probe, which means the tissue nearest the probe gets very hot and the tissue further away gets progressively less. Water vapour behaves differently, and this is the whole idea.

Turning water into steam takes a large amount of energy, and that energy is stored in the vapour rather than raising its temperature further. Injected into the prostate, the vapour disperses through the spaces between cells until it meets cooler tissue, condenses back into water, and releases all of that stored energy at the point where it condenses. The result is even destruction throughout the treated zone rather than a hot centre and a cool edge — and, because the vapour disperses along tissue planes, it stops where those planes stop, which is what spares the structures outside the treated zone.

What happens during the procedure

• The prostate is inspected through a telescope and the number of injections is decided from what is seen — the shape and size of the gland, and whether a middle lobe is obstructing.
• The needle enters roughly a centimetre into the tissue. It is finer than the needle used for a blood donation.
• Each burst of vapour lasts a matter of seconds. The whole procedure takes minutes.
• In the published pivotal study the prostate had reduced in volume by around 29% at six months.

What that percentage does and does not mean

It is a genuine published figure, and it is worth understanding what it measures. Volume reduction is not the same as symptom relief. A gland can shrink usefully while symptoms persist, if the obstruction was in a part not treated or if the bladder itself is the problem. Conversely men often feel better before six months, as swelling settles and the channel opens, long before the full volume change has occurred. Judge the treatment on how you are passing urine, not on a repeat scan.

Recovery — including the difficult part

This is a day-case procedure and men go home the same day. What the earlier version of this article did not say is what the next few weeks feel like.

• A catheter is needed for a few days, because the treated tissue swells before it shrinks.
• The first two to three weeks are commonly worse than before treatment — burning, urgency, frequency, and blood or debris in the urine. This is the expected course, not a sign of failure.
• Clear improvement usually appears by around three months and continues to settle afterwards.

The limitations

• No tissue is obtained. Prostate resection produces a specimen the pathologist examines, and cancers are occasionally found that way. Vapour therapy destroys tissue in place and yields nothing to examine, so anything suspicious — PSA, examination findings, imaging — must be resolved before the procedure rather than after it.
• Gland size determines how strong the evidence is. The trials that established this treatment enrolled prostates of roughly 30 to 80 mL, and that is where the published data is firmest. Treating up to around 120 mL is reasonable in practice, on weaker evidence and by individual judgement. Above that, resection or enucleation is generally the better operation. A larger gland is not automatically excluded — it simply means being treated where the evidence thins out, which is worth knowing before you decide.
• Long-term data is shorter than for resection, which has decades behind it. A minority of men need a further procedure within five years.
• It treats the prostate, not the bladder. Where symptoms come from an overactive or underactive bladder, shrinking the prostate will not fix them — which is why assessment before treatment matters more than the choice of technology.

Symptoms that need attention the same day

In an emergency in Thailand, call 1669.

• Complete inability to pass urine with a painful full bladder.
• Fever or shaking chills after the procedure.
• Clots blocking the flow. Lightly blood-stained urine in the early weeks is expected; clots that stop you passing urine are not.
• A catheter that stops draining or falls out early.

Dr. Soarawee introduced Rezum water vapour therapy to Cambodia. More on his clinical innovations and international milestones.

Frequently Asked Questions

Q1: How does water vapour shrink the prostate?

Vapour injected into the gland disperses between the cells, meets cooler tissue, and condenses back into water — releasing the large amount of energy that was stored when the water was turned to steam. That released energy kills the cells in the treated zone evenly. The body then reabsorbs the dead tissue over the following weeks and months, and the gland shrinks from within.

Q2: Is it painful?

Not during the procedure, which is done under sedation or anaesthesia and takes minutes. Afterwards is a different matter: burning and urgency for two to three weeks are usual, and men should expect a difficult fortnight rather than immediate relief.

Q3: Who is a good candidate?

Men with bothersome symptoms from benign enlargement who want to protect ejaculation. On size, the trials enrolled prostates of roughly 30 to 80 mL, which is where the evidence is strongest; treating up to around 120 mL is reasonable in practice on weaker evidence and individual judgement, and above that resection or enucleation is usually the better operation. Previous prostate radiotherapy and recurrent urinary infection are reasons for caution. Assessment includes measuring the gland, testing the flow, and confirming that the prostate — rather than the bladder — is the source of the problem.

Q4: Does it affect sexual function?

Preservation of sexual function is its principal advantage: ejaculation is retained in the great majority, whereas most men no longer ejaculate externally after prostate resection, and erectile function is generally unaffected. That is a strong advantage rather than a guarantee — an earlier version of this article stated there was no erectile dysfunction problem at all, which overstated it.

Q5: If my prostate shrinks by about a third, will my symptoms improve by a third?

No — the two do not track each other. Volume reduction is what a scan measures; what matters is the flow and how you feel. Some men improve well before the volume change is complete, and a few see the gland shrink without much symptomatic benefit, usually because the bladder was contributing.

Q6: Can prostate cancer be detected during the procedure?

No. Unlike resection, no tissue is produced for the pathologist. Any concern about cancer — from PSA, examination or imaging — must be investigated and settled before vapour therapy is planned.

Arranging a consultation

Dr. Soarawee Weerasopone sees patients at Bangkok Hospital Headquarters and at Samitivej Sriracha Hospital in Chonburi on 088-022-1445. Bring any previous prostate measurements, flow tests and PSA results.

Bangkok Hospital Telemedicine is available for patients who cannot attend in person, including international patients — arrange it in advance by email to the Urology department at bhquro@bdms.co.th. Samitivej Sriracha is in-person only. Enquiries about cost are answered by the hospital, not by this website.

Disclaimer: This content is written and reviewed by Dr. Soarawee Weerasopone, a board-certified urologist at Bangkok Hospital Headquarters, and is intended for education only. It is not medical advice, diagnosis or a prescription for any individual, and no advice, diagnosis or prescription is given through personal messaging channels or social media. Dr. Soarawee operates no public social media account; any account offering private consultation in his name is fraudulent. In an emergency in Thailand, call 1669.