Also, I agree with slow_healer. Try to use a SHEER or SMOOTH condom during anal sex. Ribs tend to work their way off.
Unprotected, vaginal-to-anal is pretty much risk-free, however anal-to-vaginal is a huge NO-NO! It will almost certainly cause a PH imbalance related infection.
In any sexual event like anal-to-vaginal, multiple partners or golf, there's the golden rule of thumb: "Changing hole? Change the sheath!"
...then hit the shower.
My wife & I both enjoy taking and giving anal sex.
At first I was wary when she showed me a strap-on, yet she had a valid point: if I won't do it, how could I expect her to?
We 'trained' together ...not as weird as I thought it would be, and she took my 'anal cherry' first, listening to my instruction and exclaimations. This was the most important part; I knew what she'd go through and had the advantage of a real penis that can feel! Knowing what to expect, we eased in easily, oddly romantic, comfortably and most of all, safely!
We've '***' a long way since those first experiments, but always remember good hygene.
Simply put, anal sex is safe and fun if, like all other aspects in life, preparation and maintenance are well practised!
...or "If you're going to do something irresponsible, at least do it responsibly!"
tabingins911, Are you replying to me or the OP?
I don't know about sperm cells wreaking havoc on the colon, but would like to add that you should always use a condom during anal sex, and never go back and forth between anal and vaginal.
Do some research. I've read that sperm actually destroys cells in the colon, causing anal cancer.
http://en.wikipedia.org/wiki/Anal_sex
I know , not done right can be a pain in the butt .
The anus is too important to the function of the body to experiment with. It's ment for exit only.
The point at which is becomes dangerous is when you get rough or impatient. The point at which it becomes taboo depends on your attitude. For some people this post would be taboo. If you are not rough, take your time in entering (start slowly with a finger, give the skin time to stretch - LOTS of time - and use lots and lots of lube), and accept that no means no sometimes no matter how patient you are, you'll be fine. Permanent damage may arise from anal tearing (which would result from not lubing enough or going too quickly), the compounding of fecal matter in the rectum, and deep thrusting such that the sphincter in the upper rectal cavity is bruised. Women (and men) can't just tell their bowels to stop and back up for an hour, which is why sometimes no matter how patient you are, it's just not going to happen. As far frequency, once or twice a month should not be harmful (since the anus will get a break and be able to revert back to its natural state). However, I'm not a doctor and would recommend doing some more research of your own if you want to play it safe. Good luck.