Nonoxynol-9 (often abbreviated simply as N9) is the most common spermicide on the market, and it’s available in various gels, vaginal inserts, and lubricants. It’s an extremely popular chemical; if you’ve ever bought a condom with a spermicidal lubricant, you’ve probably used nonoxynol-9.

While many people use spermicides to prevent pregnancy, it’s important to note that nonoxynol-9 is not effective at preventing any type of sexually transmitted infections. In fact, recent studies suggest that nonoxynol-9 may increase the chances of HIV transmission.

If you’re considering a product with nonoxynol-9, you should understand how the substance works–and how it can increase your chances of contracting certain sexually transmitted infections.

What Does Nonoxynol-9 Do, and Is It Safe?

Nonoxynol-9 is a surfactant, which means that it lowers the surface tension of liquids. In perfect conditions, this prevents sperm from moving towards the egg, reducing the chances of conception.

Unfortunately, N9 can also cause topical irritation, and while side effects are rare, they can include vaginal burning and itching. Nonoxynol-9 may also raise risks of yeast infections and urinary tract infections, particularly in women who are already susceptible to these conditions.

So, given these risks, are lubricants and other products with N9 at least effective? Not especially–according to information from the World Health Organization, spermicides are one of the least effective types of contraceptives. Nonoxynol-9 and other spermicides have an 18 percent failure rate–and that’s when they’re used properly.

With that being said, spermicides can reduce your risk of pregnancy, but according to the Centers for Disease Control and Prevention, condoms and other forms of contraception are much more effective choices.

Products with Nonoxynol-9 and HIV Transmission

The irritation mentioned above can be problematic, because it may increase the chances of blood-on-blood contact. As you probably know, HIV passes through the blood, and research suggests that N9 may increase the chances of contracting HIV through vaginal sex.

It’s potentially a serious risk, and in 2007, the United States Food and Drug Administration began requiring manufacturers to place warnings on products containing N9 explaining that the chemical may raise the risk of HIV/AIDS transmission.

The World Health Organization (WHO) also released a review in 2003, noting that “nonoxynol-9 is not effective in preventing the acquisition of HIV” and “based on the current evidence nonoxynol-9 use cannot be promoted for HIV/AIDS prevention programmes in any country.” WHO has also recognized that N9 might increase the risk of HIV transmission.

Here’s the bottom line: if you have HIV/AIDS or if you are at high risk of contracting HIV, you should avoid lubricants and other products with nonoxynol-9. The risks are much greater than the benefits. Do not use N9 if you have sex with multiple partners, and only use it for vaginal sex, not for anal or oral sex.

If you’re having sex with a trusted partner and you’re both tested for sexually transmitted infections on a regular basis, you can use lubricants with nonoxynol-9 safely, but remember that condoms and birth control pills are statistically much more effective. If you experience any side effects, stop using N9 immediately.