Whenever we talk about what condoms are made of, we usually limit the conversation to the condom itself, namely whether it is made of lambskin, latex, polyurethane, or other synthetic materials such as AT-10 resin and polyisoprene.

But these are not the only ingredients you'll find in a typical condom. Some of the invisible additives can cause unexpected reactions to either one or both partners, and there is often little way of knowing what you are being exposed to even after reading the product label.

To this end, here are some of the ingredients most commonly found in popular condom brands.

Nonoxynol-9

Nonoxynol-9 is a spermicidal detergent that not only helps prevent pregnancy but is able to kill many sexually transmitted infections (STIs). While effective, the frequent use of nonoxynol-9 can cause inflammation of the cervix, vagina, and rectum, undermining their cellular integrity and increasing the permeability of delicate mucosal tissues.

These types of irritations can actually increase your vulnerability to STIs, especially if you don't use condoms consistently.﻿﻿ The inflammatory reaction in women is also linked to an increased risk of urinary tract infections.

A number of condom manufacturers, such as Kimono Condoms, have made the point of removing nonoxynol-9 from all of their products. Others, such as the Trojan Armor Series, warn against the use of nonoxynol-9 condoms for anal sex or more than once-daily vaginal sex. By contrast, the majority of manufacturers do nothing to warn customers about the potential nonoxynol-9 risk.

Parabens

Parabens are a type of preservative used in many personal lubricants and lubricated condoms that inhibit bacterial growth and help extend the shelf life.

While the evidence is far from conclusive, parabens are believed by some to enhance the potential for certain types of cancer. This is because parabens have the ability to bind to estrogen receptors and interfere with normal hormonal activity. By penetrating intact skin, parabens can potentially accelerate the growth of hormone-receptor-positive breast cancers or even affect the quality and quantity of sperm production in men.﻿﻿

Whether the relatively small amount of parabens found in condoms can cause these effects is the subject of ongoing debate.

Glycerin

Glycerin is a sweet-tasting preservative classified as a sugar alcohol. It is commonly used in personal lubricants and flavored condoms to improve taste during oral sex.

The ingredient offers no protective benefit and can even increase STI risk by promoting infections like bacterial vaginosis. The sugar provides the fuel growing colonies of bacteria and/or fungus need, while disrupting the pH balance of environmental flora.﻿﻿

This may not only increase a woman's risk of getting HIV, but it can also increase the risk of spreading the virus, as well. This is because vaginal inflammation increases a phenomenon known as viral shedding, in which HIV concentrations are greater in tissues that are actively inflamed, reddened, and swollen.﻿﻿

Casein

Many manufacturers will add a milk protein called casein to their latex condoms to make them smoother. This alone makes them problematic to the ethical vegan. Since there are no international or federal regulations governing vegan certification, only a handful of manufacturers have certified that their condoms are animal-product-free with a governing body such as the Vegan Society. Among them:

L Condoms

Glyde Condoms

Sir Richard's Condoms

RFSU Condoms

Condomi Condoms

Fusion Condoms

Durex Avanti Ultima Condoms

Pasante Condoms

Even if a person is non-vegan, there is a risk, albeit slight, of an allergic reaction in persons with a known milk allergy.

Benzocaine

Benzocaine is a topical anesthetic used in certain condoms to decrease sensitivity and increase comfort during intercourse. Common side effects of benzocaine may include localized inflammation, irritation, and dryness. As benzocaine is readily absorbed through the skin, it has the potential, albeit rare, of causing dizziness, rapid heartbeat, and breathing difficulty.﻿﻿

Benzocaine is often accompanied by other tissue-stimulating ingredients such as menthol which can promote vaginal and rectal lubrication but can also cause local itchiness.

A Word From Verywell

The above-listed ingredients are only a short list of add-ins you may expect to find in your typical condom. Others include aloe vera, L-arginine, and synthetic chemical flavorings which are typically undertested for safety in vaginal or rectal tissues.

Moreover, since condoms are not regulated by the U.S. Food and Drug Administration in the same way that pharmaceutical drugs are, there is often a vast disparity in how condom products are labeled. In fact, it is not uncommon to find a specialty or novelty condom with absolutely no information as to whether it is even made of latex, lambskin, or polyurethane.

This not only places you at risk of an allergy (most especially a latex allergy), it can entirely undermine the protective benefit of a condom, increasing rather than decreasing the risk of STIs.

If uncertain about which additives a condom may contain, start by reading the label and avoiding those that offer no information at all. If unclear about what an ingredient is (or what a non-specific term like "spermicide" or "pleasure-stimulating" actually means), pick up the phone and call the manufacturer.

The more you know about the condoms you use, the better protected you will be.