Just wondering if a lost tampon can prevent you from becoming pregnant?

Lost ?: The concept is interesting. Did you ever hear of toxic shock syndrome, the deadly condition related to staph infections in certain types of tampons in the 80's...If you had a retained tampon it would eventually cause a raging vaginitis and the total body smell would be horrendous. It can be a temporary barrier but it is not going to hang around and cause unexplained infertility.

No: Your lost tampon would be somewhere in the vagina but not blocking your cervix, which is the door to your uterus and entry to fertilization. The lost tampon can become a source of serious infection though, so see your clinician if necessary so you can get it out.