Q: I recently had oral sex, and I was wondering if saliva has any spermicidal properties?
A: Spermicides are substances that kills sperm and are commonly used on condoms, diaphragms and other contraceptives to try to reduce the chance of a couple getting pregnant. It is true that saliva can kill sperm, since saliva does contain small amounts of stomach acid (which help to pre-digest food). However, saliva is 99.5% water, so it's relatively safe for sperm. In other words, saliva will only kill a small amount of sperm, leaving most of the 150 million sperm that is released in an average ejaculation unharmed. There is some research that the sticky quality of semen can impede the movement of sperm, but this was found to be a pretty weak effect; again, only affecting a minority of sperm. So, saliva doesn't kill or impede sperm enough to act as a spermicide or other form of contraceptive.
Answers provided by Dr. Ross Avilla
Dr. Ross Avilla has been teaching Human Sexuality since 2013 and has a PhD in psychology from UC Davis. Dr. Avilla is not a clinician and all information and advice offered on this website is for educational purposes only.