It seems that every website on sexual health advises against using oil-based lubricants with condoms. It is claimed that "oil breaks down latex". One source claimed that a latex condom completely breaks down in only 60 seconds. It made me curious, so I made an experiment.

I took a piece of rubber latex condom and soaked it into regular canola oil I found in the kitchen. I checked the condom after 1 minute, nothing changed. So I let it soak for about 5 minutes more, and then 5 hours more, still nothing. It was able to hold a large amount of water without leaking or breaking.

So I am wondering, is it really true that oil degrades latex? What sort of chemical reaction is supposed to happen? What properties of the latex material and the oil influence this reaction?

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    $\begingroup$ As far as I know the issue only applies to latex condoms (made from natural rubber). Many oily solvents degrade rubber's integrity. But not all condoms are latex; some modern ones are polyurethane and have totally different characteristics with solvents and lubricants. $\endgroup$ – matt_black Dec 31 '13 at 13:26

First off, may I say that I applaud your decision to test this through an experiment. It's rare to see that than I would like.

Now, on to the matter at hand. It's fairly well known from industrial chemistry that non-polar solvents degrade latex quite heavily.

I work with latex seals a lot, and the hexanes we use routinely break the seals down in under a day. Of course, if you're lubricating your condoms with hexanes, you're a) an idiot or b) absolutely insane.

A paper I managed to find suggests that there really isn't too much direct data on condoms, and it muses that the warnings might have arisen from industry, where nonpolar solvents decidedly do degrade latex.

To find out, they did a burst experiment with condoms that had been treated with various oils. Glycerol and Vaseline-treated condoms showed a very, very minor decrease in strength, while mineral oil/baby oil-treated ones burst at less than 10% of the volume of an untreated condom.

They also found that 10 month-old condoms have half the burst volume of 1-month old ones, so you could argue that using 1-month-old condoms that have been slathered in Vaseline is still much safer than using older ones.

As for the actual chemistry of the weakening, I honestly don't know. If I were to hazard a guess, I would note that the latex looks like a bunch of ethylenes glued together,

so my guess would be that the solvents get between the chains and force them apart, weakening them. For this to happen, the solvent must be nonpolar, but still small enough to slip between the chains of the polymer.

That's probably why vaseline and canola oil don't have much of an effect---they're just too big to fit between the chains. Again though, I don't know for sure, so don't quote me on this last paragraph.

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    $\begingroup$ Rubber isn't that much like polyethylene. It is, in effect, the polymer cis-1,4-polyisoprene (which contains unsaturated bonds in the polymer backbone). It doesn't contain aromatic rings as in the example drawn which looks more like the copolymer of styrene and butadiene, an artificial polymer unrelated to condoms or natural rubber. $\endgroup$ – matt_black Dec 31 '13 at 13:32
  • $\begingroup$ Biologist here. Mineral oil is composed of alkanes. Coconut oil is largely triglycerides. Other than the fact that we call both of these products "oils," I can't see why they'd exhibit similar reactiveness with latex. In fact, I'd suggest the triglycerides are more similar to silicone oils than to mineral oil. However, I am neither a materials scientist nor a chemist. $\endgroup$ – Juno Woods Jul 5 '16 at 20:11
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    $\begingroup$ @Dr.JohnnyMohawk Chemist here. You can basically consider any triglyeride a long, triangular (i.e. once branched) alkane chain. The main difference are six oxygen atoms somewhere in the middle that don’t contribute much to the overall hydrophobicity ;) $\endgroup$ – Jan Aug 24 '16 at 9:52

If you put a jelly baby in water, it does not dissolve, but swells to five time it's original size, and becomes very soft and brittle.

Same happens to rubber in oil. It is a crosslinked polymeric material, and when all the bonds in the network are completely stretched due to a solvent that has diffused in, they cannot take any additional strain, and break very easily. No chemistry is involved, the rubber just tries to dissolve, but cannot get away except by breaking.

Depending on the oil you use, and the temperature (37°C might be worse than 20), the effect can be more or less pronounced. Hexane or petrol will destroy the condome most efficiently, trigylcerides, which are slightly more polar and cannot efficiently diffuse into the rubber network because they are large and have a bulky side chain (=the middle fatty acid), somewhat less.


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