An estimated 28 out of 100 women who use spermicide alone will get pregnant in the first year of typical use. Spermicide is more effective at preventing pregnancy when used with a barrier method of birth control.
Spermicide may increase the risk of urinary tract infections. Vaginal irritation — such as burning or itching or a rash — is the most common side effect of spermicide. It's also possible to have an allergic reaction to spermicide.
Spermicide doesn't offer protection from sexually transmitted infections. In fact, frequent use of spermicide may increase vaginal irritation, which may increase the risk of contracting HIV or other sexually transmitted infections. Similarly, spermicide shouldn't be used rectally because it may cause irritation and increase the risk of contracting sexually transmitted infections.