My philosophy has been that a little dirt won't hurt, but when it comes to something where things like E.coli and Salmonella can live, I try to be more diligent--i.e. the kitchen. We made sure to sterilize the bottles and my pump parts on a weekly basis, and more frequently in the first 3 months (didn't have bottles or pump, but did have pacifiers). As they get older, its much less worry, as their immune systems become much stronger. I am much less cautious at home than I am when out and about too--because I know what our germs are, kwim?