Why are condoms only 99.9% effective?

No it is because some stds are small enough to go right through condums that is why. And birth control is because some times your stomoch produces anty bodys (my mom got pregnant with my brother on birth control)

Another failure point during actual use (as opposed to correct use) is not putting it on at the right time. The penis leaks pre-come when the guy is aroused, and pre-insertion snuggling can allow some of this leakage to be left at the lips of the vagina, which can (low %) be problematic. And of course there is the “…let me just put it in just for a minute…” plea from over eager, clueless guys.

If you ever are in the situation of condom breaking or slipping off, if you take the morning after pill, your chances of conceiving will be reduced by 70-85% if the pill is taken within 72 hours. (And some authorities say it might help up to 120 hrs.) In the US it is called Plan B, but around the world there are other brands.

Take care of yourself, and Good Luck!!

condoms are only 97% effective if used correctly, not 99% the pill is 99% effective at preventing pregnancy if used correctly the condom is only 97% effective and no, not just breakage there are things that affect how likely it is to break keeping it in a wallet for a long time for example, or using 2 condoms at the same time all make the condom more prone to breaking no contraception or birth control s 100% effective so theres a 1% chance that it wont work also how you use it affects its affectivness most people dont use them correcty so they have a higher chance of getting pregnant certain lubricants or things people use as lubricant can affect them as well if you use them past there expirey date they also have a higher chance of not working