A condom is a thin, flexible sheath worn during sex to prevent pregnancy and reduce the risk of sexually transmitted infections (STIs). It works as a physical barrier, keeping sperm and infectious fluids from passing between partners. There are two main types: external condoms, which fit over the penis, and internal condoms, which are inserted into the vagina or anus before sex.
External vs. Internal Condoms
External condoms are the more widely known type. They unroll over an erect penis and collect semen during ejaculation, preventing it from entering a partner’s body. Most are made of stretchy material with a reservoir tip at the end.
Internal condoms are pouches with a flexible ring at each end. One ring sits inside the vagina or anus to hold the condom in place, while the other ring stays outside the body, covering part of the external genitalia. Internal condoms give the receptive partner more direct control over barrier protection. Both types are single-use and should never be reused or worn simultaneously.
What Condoms Are Made Of
Most condoms are made from natural rubber latex, which has been the standard material for decades. Latex is highly elastic, strong, and effective at blocking both sperm and viruses. The main downside is that some people are allergic to it, experiencing itching, redness, or a rash during or after use.
For those with latex sensitivities, two synthetic alternatives exist. Polyisoprene is a soft synthetic material that mimics the stretch and strength of latex without triggering latex allergies. It’s become a popular option, sold under brands like SKYN. Polyurethane is a thinner, stiffer plastic that also works for people with latex allergies and has an added advantage: it’s compatible with oil-based lubricants, which damage latex. Polyurethane condoms can feel less elastic, but their thinness may enhance sensation for some users.
A fourth type, made from natural animal membrane (usually lamb intestine), also exists. These prevent pregnancy but do not reliably protect against STIs. Lab testing has shown that viruses can pass through tiny pores in the membrane. In one study, roughly half of natural membrane condom samples leaked a small virus, and a smaller number leaked larger viruses like herpes. If STI protection matters to you, latex or synthetic condoms are the better choice.
How Well Condoms Prevent Pregnancy
Condom effectiveness depends heavily on how consistently and correctly they’re used. With perfect use, about 2 out of 100 women whose partners use external condoms will become pregnant over the course of a year. With typical use, which accounts for real-world mistakes like putting the condom on late, using it inconsistently, or not leaving space at the tip, that number rises to about 15 out of 100.
The gap between those two numbers is entirely about human error, not the condom itself. Using a condom correctly every single time closes that gap significantly.
Protection Against STIs
Condoms are one of the most effective tools for reducing STI transmission, though protection levels vary by infection. External condoms offer more than 90% protection against HIV and hepatitis B when used consistently. Protection against gonorrhea falls in the 49 to 75% range based on cross-sectional studies, while consistent use reduces chlamydia risk by roughly a third.
Infections spread through skin-to-skin contact in areas a condom doesn’t cover, like herpes (HSV-2) and HPV, see lower protection rates, typically in the 10 to 50% range. That’s because the virus can shed from skin around the genitals that the condom doesn’t touch. Still, consistent condom use reduces risk for these infections too, just not as dramatically as for fluid-borne infections like HIV.
Choosing the Right Size
Fit matters more than most people realize. A condom that’s too tight is uncomfortable and more likely to break. One that’s too loose can slip off during sex. External condoms are sized by their nominal width, which is the diameter of the opening when laid flat. In the United States, most manufacturers group their sizes into three categories:
- Small (snug or slim): 49 to 52 mm nominal width
- Regular (standard): 52 to 56 mm nominal width
- Large: 56 to 60 mm nominal width
There’s no universal labeling standard, so a “regular” from one brand may fit differently than a “regular” from another. If a condom feels uncomfortably tight, leaves a red ring, or feels like it could slide off, try a different size. A properly fitting condom should feel snug but not restrictive, and it should stay in place without effort.
Lubricant Compatibility
Using lubricant with a condom reduces friction, makes sex more comfortable, and lowers the chance of the condom tearing. But the type of lubricant matters. Oil-based products like baby oil, body lotion, coconut oil, and petroleum jelly break down latex. Lab testing has shown that mineral oil-based lubricants cause significant latex degradation, weakening the condom and increasing the chance of failure.
Water-based lubricants are safe with all condom types. Silicone-based lubricants are also safe with latex, polyisoprene, and polyurethane condoms. If you’re using polyurethane condoms specifically, oil-based lubricants are an option since polyurethane isn’t affected by oil. For latex and polyisoprene, stick with water-based or silicone-based products.
How Condoms Are Tested
Condoms go through rigorous quality testing before reaching consumers. International standards set by the WHO and ISO require manufacturers to test for two critical properties: airburst strength and freedom from holes. In airburst testing, condoms are inflated until they pop, measuring how much air volume and pressure they can handle. Freedom-from-holes testing checks for microscopic defects, either by filling condoms with water and looking for leaks or by using an electrical test that detects tiny openings.
The acceptable defect rate for holes is set at just 0.25%, meaning fewer than 3 condoms per 1,000 can have a detectable hole and still pass inspection. Condoms that fail any critical test cannot be sold.
Storage and Shelf Life
Condoms degrade over time, especially when exposed to heat. The WHO recommends that condoms be stored at average temperatures below 30°C (86°F) and never exposed to temperatures above 50°C (122°F), even briefly. That means keeping condoms in a wallet, glove compartment, or back pocket for extended periods is a bad idea, since body heat and direct sunlight can weaken the material.
Every condom has an expiration date printed on the wrapper. Latex condoms typically last several years from the date of manufacture when stored properly, but their shelf life is determined by real-time testing at controlled temperatures. Always check the date before use. If a condom feels brittle, sticky, or dried out when you open it, discard it and use a fresh one.