What are the causes for bladder infections? and any ways of prevention?

friend of mine gets bladder infections very easily, always after sex.....she does empty her bladder before and after sex and drinks plenty of water and tries to use urinary alkanizer's, doctors prescribe antibiotics but the problem continues to return.....any ideas??? i live in Australia

I am referring to intercourse induced bladder infections.
That happened to me 25 yrs ago tried all the usual stuff. Start with clean genitalia,pee after,use a water rinse . Like sit on toilet and run a stream of water over the area.after intercourse. Change the position of intercourse to press less on the urethra. Now after all of that said. I too did the antibiotic thing. Was about to do the antibiotic after intercourse. But what happened was the doctor did a procedure. He inserted a catheter up the urethra,filled it with saline. Drained it and then inserted a long thin metal device and he opened the device up to spread my urethra area. It was extremely painful. Now days they would give pain meds. if they still do this procedure. It worked never had a infection since then. Something about the urethra and the muscle that the bladder uses. It was too small or the muscle was too tight. I don't know just that it WORKED.

*Drinking lots of cranberry juice and other acidic drinks
*Wipe front to back to prevent spread of bacteria
*Breathable cotton undereear and not skin-tight clothes
*Use unscented soap in the shower
*Pee often. Even if you don't think you have to, go every few hours at least.

"If having sex seems to cause your infections, your doctor may suggest that you take a single antibiotic pill after you have sex to prevent urinary tract infections."
http://familydoctor.org/x5180.xml

Katie forgot only one thing...Is it possible that your friends partner is the problem?? He should be tested maybe he has some bacterial infection and keeps giving it to her.

I used to have the same problem for 3 years. Mine didn't have a cause. Some people are just prone to them. Taking at least 1000 mg of Vitamin C a day completely cured the problem. It makes it so bacteria cannot live in the urine. If you start getting symptoms take Golden Seal. It's an herb. Cranberry juice can make them worse because of the sugar.

Your Friend could drink Cranberry Juice this does work