Nonoxynol-9
Nonoxynol-9, sometimes abbreviated as N-9, is a non-ionic nonoxynol surfactant that is used as an ingredient in various cleaning and cosmetic products, but is also widely used in contraceptives for its spermicidal properties.
Although it was at one time widely promoted as a protection against sexually transmitted infections including HIV, subsequent studies have shown that it can in fact increase the risk of infection by damaging the physical barriers of the rectum or vagina.

# Uses

## Spermicide
As a spermicide, it attacks the acrosomal membranes of the sperm causing the sperm to be immobilized.
Nonoxynol-9 is the active ingredient in most spermicidal creams, jellies, foams, gel, film, and suppositories.
A 2004 study found that over a six-month period, the typical-use failure rates for five nonoxynol-9 vaginal contraceptives (film, suppository, and gels at three different concentrations) ranged from 10% to 20%.

## Condoms
Many models of condoms are lubricated with solutions containing nonoxynol-9. In this role, it has been promoted as a backup method for pregnancy and STI prevention in the event of condom failure.
However, the 2001 WHO/CONRAD Technical Consultation on Nonoxynol-9 concluded that:
There is no published scientific evidence that N-9-lubricated condoms provide any additional protection against pregnancy or STIs compared with condoms lubricated with other products.  Since adverse effects due to the addition of N-9 to condoms cannot be excluded, such condoms should no longer be promoted.  However, it is better to use N-9-lubricated condoms than no condoms.
Additionally, the WHO statement suggests that N-9 should not be used rectally under any circumstances.

## Cervical barriers
Almost all brands of diaphragm jelly contain nonoxynol-9 as the active ingredient.  This jelly may also be used for cervical caps and Lea's shields.
Most contraceptive sponges contain nonoxynol-9 as an active ingredient.

## Shaving Cream
Nonoxynol-9 is sometimes included in shaving creams for its properties as a nonionic surfactant; it helps break down skin oils that normally protect hair from moisture, so that they become wet and, hence, softer and easier to shave. Gillette formerly used nonoxynol-9 for this purpose in its Foamy products, but has discontinued the practice.

## Sports Cream
Nonoxynol-9 is also found in Bengay Vanishing Scent as an inactive ingredient.

# Side effects
Nonoxynol-9's ability to kill microbes in vitro was initially taken as evidence that it might be effective at preventing STI transmission. However, more recent findings indicate that it may actually increase a person's risk of contracting STIs, especially if used frequently. This is because the chemical causes tiny abrasions inside the sensitive vaginal and anal walls.  These abrasions may make transmission more likely especially if condoms are not used.
From 1996 to 2000, a UN-sponsored study carried out in several locations in Africa followed nearly 1000 sex workers who used nonoxynol-9 gels or a placebo. The HIV infection rate among those using nonoxynol-9 was about 50% higher than those who used the placebo; those using nonoxynol-9 also had a higher incidence of vaginal lesions, which may have contributed to this increased risk.  Regular use of nonoxynol-9 likely increases the risk of infection with sexually transmitted human papillomaviruses (HPVs) that can cause cervical cancer. While these results may not be directly applicable to lower-frequency use, these findings combined with lack of any demonstrated HIV-prevention benefit from nonoxynol-9 use have led most major health agencies to recommend that it no longer be used by women at high risk of HIV infection. The WHO further notes that "Nonoxynol-9 offers no protection against sexually transmitted infections such as gonorrhoea, chlamydia."
Nonoxynol-9 based products (including condoms containing the spermicide) should not be used for prevention of HIV or STDs or for contraception between non-monogamous partners because of the increased risk of infection by HIV or sexually transmitted infections.  However, non-spermicide condoms are available and are still highly successful at preventing both pregnancy and STD transmission.
Frequent use of nonoxynol-9 is linked to higher risk of urinary tract infections (UTIs).
Some people have reported allergic reactions to Nonoxynol-9; however, it is possible to test it oneself on the lymph nodes on the upper thigh by the groin to see if one is hypersensitive. If so, the skin usually turns red and causes a burning sensation. Recovery  from an allergic reaction usually takes about 6-8 hours.

# Alternatives
Chemically speaking, there are two alternatives to nonoxynol-9 spermicide:
- Menfegol:  Available as a foaming tablet in Europe.
- Benzalkonium chloride: Stand-alone benzalkonium chloride spermicide is only available in Canada and Europe (Hungary) and limited to pessary form. Benzalkonium chloride is also the active ingredient in one brand of contraceptive sponge, available only in France.
For use with a cervical barrier such as a diaphragm, a jelly containing lactic acid may work as a substitute. 
Lactic acid is known to immobilize sperm, also. But in contrast with nonoxynol-9, this immobilization seems to be reversible and is for that reason less reliable.