Joe Barsugli points out a potentially dangerous casual comment in my blog entry on Condoms and AIDS. I wrote that I vaguely remembered that spermicides kill HIV potentially preventing infection even if condoms leak. Joe writes

"... your info on spermicides (Nonoxynol-9) is out of date. It is currently thought that N9 increases the chance of HIV transmission (because of irritation), at least for anal sex."

Joe is an atmospheric scientist, so he isn't an officially qualified expert.

More generally I think I should remind the reader that these are random thoughts. No one should make important health decisions based on the top of the head thoughts of an economist or even, I suppose, the informed comments of an atmospheric scientist.

Anyway thanks Joe.