膀胱感染（膀胱炎）：なぜあなたに起こったのか

最終更新日: 2026年8月15日

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A great many patients come to my office with a bladder infection — 急性膀胱炎 in medical terms — and nearly all of them ask the same question: why me? For some it is the first time; for others it has been happening on and off for years. This article answers that question by explaining how bacteria actually get into the bladder, because once you can picture the route, both the risk factors and the prevention make sense.

What it feels like

• Burning or pain on passing urine
• A strong, persistent urge to go
• Passing small amounts, frequently
• Pressure and pain low in the abdomen
• Blood in the urine — uncommon, and alarming when it happens, but not in itself a sign of anything worse

Two things change the picture and mean you should be seen the same day rather than waiting: a fever, または pain in the back or flank. A simple bladder infection does not cause either. Both suggest the infection has travelled up to the kidney — 急性腎盂腎炎 — which is a far more serious illness and needs prompt treatment.

How the bacteria get in

Bladder infection overwhelmingly affects women: about 10% of women have one each year, and most women will have at least one episode in their lifetime. The reason is anatomical — the female urethra is short, and its opening sits close to the anus.

The usual culprit is 大腸菌, a bacterium that lives harmlessly in the large intestine and causes no trouble at all while it stays there. After a bowel movement it can settle on the perineum and vagina, and from there it climbs the urethra into the bladder, using tiny surface appendages to grip the bladder lining rather than being washed away.

The body is not defenceless. Simply passing urine flushes bacteria out mechanically, and the immune system attacks what remains. But some strains of 大腸菌 hide inside the cells of the bladder wall, where neither the immune system nor an antibiotic reaches them easily. That is what tips the balance into infection — and it is also why infections come back in some women and not others.

When it stops being a one-off

A simple bladder infection should not happen more than twice in 6 months or three times in a year. Past that threshold it is called 再発性膀胱炎, and it deserves proper investigation rather than another antibiotic course — there is often a correctable reason behind it.

What actually prevents the next one

• Drink more than 2 litres of water a day, enough to keep your urine pale yellow or clear. This is the simplest and most effective measure there is — it works by flushing bacteria out before they can take hold.
• Do not hold on. Delaying gives bacteria more time to multiply in a warm, still bladder.
• Pass urine soon after intercourse, which flushes the urethra before bacteria can ascend.
• Where infections keep returning, several non-antibiotic measures reduce the recurrence rate — worth reading if this is a recurring pattern rather than a first episode.

排尿時の灼熱感、尿意切迫感がある場合、または膀胱炎が疑われる場合は、バンコク病院本院にてSoarawee Weerasopone医師による専門医の診察を受けることができます。. 診療をご予約。Samitivej Sriracha Hospital での予約は、泌尿器科に電話でお問い合わせください。電話番号: 088-022-1445.

膀胱炎（急性膀胱炎）に関するよくある質問

免責事項: 本コンテンツは、Bangkok Hospital Headquarters の泌尿器科専門医(board-certified)である Dr. Soarawee Weerasopone が執筆・監修したものです。教育目的のみで提供されており、医学的助言を構成するものではありません。個人宛のメッセージ手段では、医学的助言、診断、処方は一切行っておりません。いかなる治療も、開始前に必ず資格を持つ医療専門家にご相談ください。