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Dry Humping, is:

dry humping is the process of two people repeatedly moving up and down and back and forth on top of each other fully clothed( or missing various pieces, but the penis must not come in contact with the vagina with out some sort of fabric separating them ex: boxers,panties, or even sheets!!)

We all know that the basic rule for impregnation is that the sperm must come in contact with the egg, and even be able to fertilize it. While sperm can get through clothes, semen (but this is yet been proven or disproved) gets stuck, thus the sperm dies.

What is your opinion about this? If two people are on top of each other, fully clothed, and the male comes to ejaculation, is there any chance that pregnancy can happen, in the realistic and biological look at it (and not some probability or statistical way)? What advice should be given to teens on the matter?

I am a computer scientist with no biology knowledge, and am very interested in getting the opinion of biologists.

But since I know that the stackexchange community likes to see work done before asking questions, I did my own research (I am used to googling code and algorithms): Very few research has been done on the subject. There is one shining research that concluded, as I recall, that:

If the underwear is completely saturated with semen, and is in direct contact with the woman's vagina, pregnancy is possible statistically, but highly unlikely.

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If there has been an ejaculation by the male, and semen is present, there is a chance of getting pregnant. Period. Teens really need to know that.

I think you may have your terms confused - semen is the overall fluid released during an ejaculation, sperm are the cells with tails that are produced in the testes and fertilize the egg. At any rate, according to the WHO, a normal sperm count is over 15 million per milliliter, with some counts much higher (>50e6/ml ), and an average between 20 and 40 million. The volume of the ejeculate tends to be anywhere from 1-6 ml. If you take a healthy young male at the peak of his reproductive capabilities, this equates to a very large number of sperm being released during a sexual encounter. All it takes is for one to reach an egg and fertilize it. Sperm are very very small, much smaller than the pore size of average fabric, so clothing will do very little to stop them. The female is likely sexually aroused during this activity as well, and produces additional fluids and lubricants that promote the survival and motility of sperm, among other things.

So, it depends on many factors. If both parties are fully clothed (at least 4 layers of clothing between their respective reproductive organs) and there is a minumum of soaking through, the chances of pregnancy are correspondingly quite low. On the other hand, if only one partner is wearing just their underwear, it's essentially like there is no clothing present at all, and the relative chances go up significantly.

Safe sex practices can't be emphasized enough to young people, as education and awareness is so much better than ignorance and myths. Even aside from pregnancy, if condoms are not utilized properly to contain all the semen there is the chance of sexually-transmitted diseases, ranging from herpes and gonorrhea to AIDS. None of these require penetration to be passed along, and one might argue that the additional presence of potentially irritating fabrics could open up raw areas or cuts and enhance their transmittal.


Take home message

Now, all this being said, the chances of impregnation through clothing without direct penetration of the penis into the vagina is quite low compared to "typical" unprotected fully-penetrating intercourse, especially depending on where the female is in her fertility cycle. According to this study, a woman's most fertile day is two days before ovulation (as had been postulated before), and the chances of pregnancy on that day are about 25% (assuming penetrating intercourse). Overall, the chance of pregnancy throughout the month is about 5%.

I don't have any hard numbers on the pregnancy chances when one or both partners have at least some clothing on, as obviously it will vary greatly depending on who is wearing what, the volume of ejaculate, contact time after ejaculation, etc. Just for fun, let's assume it's 100 times lower. That means the chances of impregnation two days pre-ovulation would be 0.25%, or 1 in 400. While rather low, this is still a non-zero chance.

Condoms are about 98% effective if used properly during penetrative vaginal intercourse. Various other birth control methods such as contraceptive pills, intrauterine devices, implants and injections are quoted as being 99% effective on their own, although they do not protect against sexually transmitted diseases. I'm certainly not one for preaching abstinence, but done properly it should be 100% effective. Ultimately, it is up to both partners to decide what their risk tolerances are, together. It is much better to seriously talk about it beforehand than to be panicked and unsure afterwards.


Hopefully this addresses your concerns, please leave comments if you have additional questions.

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  • $\begingroup$ P.S.: I am gathering all this information in order to write a few articles, to make more teens aware of the risks. Now we know that it is certainly possible by statistics and probabilities. But realistically, considering you know all the technical information about semen and sperm. Is it realistically possible? What kind of advice would you give teens whom this way of sexual interaction is their only option? $\endgroup$ – TheNotMe Jul 29 '14 at 11:36
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    $\begingroup$ @caseyr547 could you at least explain why this is a bad answer? Comparing an answer based on scientific and medical facts to a TV show is not an answer. $\endgroup$ – MattDMo Jul 29 '14 at 20:14
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    $\begingroup$ Meh it's bad science wrapped in a lot of excuses...winning the lottery is also realistic by your math $\endgroup$ – user1357 Jul 29 '14 at 21:25
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    $\begingroup$ Matt, It likely is a bad answer. Take a look at this WebMD blog post. blogs.webmd.com/womens-health/2010/01/… from a factual perspective about pregnancy risk. $\endgroup$ – AMR Jan 23 '16 at 4:19
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    $\begingroup$ I've edited the answer to add some more information as well as some verified and off-the-cuff numbers, as well as discussed family planning in greater detail. $\endgroup$ – MattDMo Feb 22 '16 at 18:55
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It is effectively impossible to get pregnant by dry-humping because the conditions that would have to be met for sperm to pass through multiple layers of clothes, survive on skin, find the vaginal opening, survive in the vaginal environment and finally impregnate an egg are simply unrealistic.

The barrier of clothing that we can assume present during 'dry humping' is significant. Semen begins to die as soon as it begins to dry out and any clothes you're wearing are likely to draw water away from the sperm cells through adhesion of water to the fabric. One layer is absolutely not "like there is no clothing present at all".

Assuming some sperm cells made it through all that and onto skin, their motion isn't directed towards the vaginal opening, so a sizable fraction will be literally lost at that step. Skin is also a toxic environment on its own, so these improbable sperm have a very limited time to find their way.

That last battle buddy team of sperm has very little chance of surviving the vaginal environment. A lot of sperm need to enter the vaginal environment together to ensure that just a few survive.

As far as dry humping is concerned, there's no realistic reason to worry about pregnancy.

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