What happens to your body when you have sex

Despite the widespread belief that men think about sex 24/7, science says it ain't so. A 2003 study published in the Journal of Sex Research found that men think about sex an average of just 19 times per day. Refuting this stereotype was important to Terri Fisher, professor of psychology at Ohio State University and the study's lead author. "It's amazing the way people will spout off these fake statistics that men think about sex nearly constantly, and so much more often than women do," Fisher said, after releasing the study online.

While sex is more of a euphemism than an exact term, some facts just can't be ignored. From strengthening your immune system, to how aging impacts sexuality, here's what really happens to your body when you have sex — however you define it.

What is sex, anyway?

First, it's important to note there is no commonly shared consensus on what the act of sex is, according to Dr. Steve McGough, associate professor of clinical sexology at the Institute for Advanced Study of Human Sexuality. "Many consider [sex to be] intercourse involving penetration, but that clearly is only one aspect of the sexual experience," McGough told me. "Sex is often uniquely defined by each person based on their backgrounds and experiences. There are also widely held differences in what 'love' means and how it relates to sex. The combination of multiple meanings for 'sex' and multiple meanings for 'love' tend to get a lot of people confused."

One general description of the word comes from Canada's Sexuality Education Resource Centre, which defines sex as "the act of two or more people using words or touch to sexually excite themselves and/or each other." But whether you refer to the act of sex as "shagging," "makin' whoopee," or "doin' the horizontal mambo," it should go without saying that any sexual activity should only happen within the context of consent — the clearly communicated agreement between participants to engage in sexual activity, according to RAINN, the Rape, Abuse & Incest National Network.

The sexual response cycle

In the 1960s, famous researchers Dr. William Masters and Virginia Johnson observed various individuals engaging in both solo and coupled sexual activities, later publishing their findings in the groundbreaking book Human Sexual Response. The duo coined the phrase "sexual response cycle" to describe the physical and emotional changes one experiences during sex: excitement, plateau, orgasm, and resolution. Though the model is still considered the standard in clinical and educational settings, modern research suggests a different sexual response cycle for women, Dr. McGough said.

"The original Masters and Johnson definitions were based around a male paradigm, where 'arousal' was all that was needed," McGough explained. "More recent models differentiate for women by introducing the concept of desire, or the mental state that is related to attraction and [the] wish for sexual activity. Further, instead of being 'linear,' women can experience continuing series of plateau and orgasm in sequence, if they're familiar with achieving orgasms and are comfortable with their bodies and the situation."

Score one for the ladies.

Stage 1: Excitement

During the sexual response cycle's excitement stage, both men and women experience increased blood flow to their genitals. "Men tend to get an erection and women tend to have slight swelling of the clitoris, vulva, and vagina," McGough said. "Women often produce lubrication, but the amount varies. Many women [also] begin to have increased blood flow to their breasts and develop erect nipples."

Other characteristics of this phase include a heightened heart rate and accelerated breathing, according to WebMD.

Stage 2: Plateau

The period between initial excitement and orgasm is referred to as the plateau stage, McGough explained, during which the body's responses, which began in the excitement phase, continue to intensify. For example, women produce more lubrication and often develop skin flushing in the face, neck, and chest. Men can experience similar flushing, as well as hardening of the nipples. "It isn't confirmed, but [it's] widely believed nipple erection in both men and women is due to the release of oxytocin," McGough said.

At this point, overall muscle tension increases for both partners. Also notable about the plateau stage is how a woman's clitoris becomes more sensitive — in some cases, almost painful to the touch — and retracts under the hood to avoid direct stimulation.

Stage 3: Orgasm

Orgasm is the sexual response cycle's shortest phase, lasting between 10 and 25 seconds for both men and women, McGough said. The orgasm phase is generally characterized by a sudden release of tension caused by involuntary muscle contractions. For women, such contractions can be felt in the vagina, uterus, and rectum, according to the nonprofit organization Our Bodies Ourselves. Men typically experience rhythmic contractions in their prostate, often resulting in the ejaculation of semen.

"Orgasm can be just the reflex contractions in the genitals, which is pleasant, or the more common [and far more pleasurable] state where the genital's reflex contractions correspond to an intense mental state where the person momentarily becomes lost in the moment," McGough pointed out. "This brief loss of a sense of self is why the French slang for orgasm is 'la petite mort' or 'the little death.'"

Stage 4: Resolution

During the resolution phase, "the body slowly returns to its normal level of functioning." Men go through what McGough called the "refractory period," in which they naturally lose their erection and require time to recover before engaging in further sexual activity. However, some women can quickly return to the orgasm phase, particularly if they have continued stimulation in areas other than the clitoris, or if the initial orgasm occurred vaginally or elsewhere, McGough said.

You can bust the myths

Despite a plethora of scientific research about sex, fallacies about the act persist, including the assumption that women "should" achieve penetrative orgasms, or the stereotype that a woman's libido is somehow less than a man's. When a woman is unable to orgasm via penetration alone, "men just don't get it and women often feel like there's something wrong with them," McGough said. "According to The Hite Report and other studies, fewer than 30 percent of women can achieve orgasm through intercourse. My observations in talking with thousands of women over the years, though, is [that] this percentage is much smaller."

Another misconception about sex is the belief that simultaneous orgasms are the "holy grail" of sexual activity. While many people desire to have them, doing so is "not usually easy," McGough said. "I can say from extensive discussions [with clients] that most people enjoy orgasm more if they can just experience the stimulation and not worry about the details for their other partner. So if one partner has a strong orgasm and then, after enjoying the moment, takes care of the other, it's often more fulfilling."

Your brain lights up

For all the physical changes the body undergoes during sex, the brain experiences a similar flurry of activity. Doctors like Barry Komisaruk, Beverly Whipple, and others have conducted studies in which women volunteered to experience orgasm while connected to a functional magnetic resonance imaging system (fMRI). "Desire in the mind leads to arousal, which increases sensitivity in the genitals," McGough explained. "This increased sensitivity causes more stimulation to specific corresponding regions of the cerebral cortex. For women, different regions of the cortex are activated by stimulation from the clitoris, vagina, cervix, nipples, etc."

Continued stimulation activates the hippocampus and amygdala — both of which are located in the limbic system, a region of the brain associated with emotion and memory. As orgasm gets closer, the vagus nerve induces deep breathing in the belly. Komisaruk and Whipple detected the vagus nerve's role in orgasm while observing women with spinal cord injuries having orgasms via vaginal stimulation. "While women were in the fMRI, [Komisaruk and Whipple] saw the vagus nerve light up," McGough said. "Further, when orgasm occurs, the fMRI studies show a storm of activity in almost all regions of the brain. Many say the closest analogy to this [activity] is a brief seizure."

You'll get the feels

While sex can certainly be physically gratifying, recent research indicates it also helps increase emotional bonding between partners. A 2017 study of newlywed couples published in Psychological Science found that sexual satisfaction remains elevated for roughly 48 hours after sexual activity. "People with a stronger sexual afterglow — that is, people who report a higher level of sexual satisfaction 48 hours after sex — report higher levels of relationship satisfaction several months later," lead study author Andrea Meltzer told ScienceDaily.

According to McGough, the release of oxytocin that occurs during sex simultaneously causes a reduction in the stress hormone cortisol, leading to an even more relaxed feeling. "Oxytocin, the 'love' hormone, tends to cause feelings of affection and connection," McGough said. "There also tends to be increases in the sex hormones, meaning testosterone in men and both testosterone and estrogen in women. This induces a more positive state in general."

In other words, if you've ever cried after doing the deed, there's a scientific explanation for all those emotions you're feeling.

You could look younger

Where do we begin? The health benefits of both sex and intimate touching in general are far-reaching, from a reduction in respiratory illness and lower stress responses when experiencing physical pain, to stronger immune systems and better critical-thinking skills.

An especially impressive finding? In a 10-year study, British clinical psychologist Dr. David Weeks found that couples who had sex three times a week looked up to 10 years younger than their chronological age. Weeks published his findings in Superyoung: The Proven Way to Stay Young Forever.

As if you needed more reasons to get busy.

Sex changes as you age

Good news: Getting older doesn't automatically mean you can't enjoy a healthy, active sex life. In fact, increased emotional maturity in your golden years could have the opposite effect, McGough revealed. "While bodily changes do occur, many people become more accepting of themselves and their partners [as they age]," he said. "This increases the possibility for new sexual connection and intimacy. Plus, as people gain perspective on life, their understanding of 'love' and its multiple meanings broadens in how it applies to sex."

Normal physical changes are one thing, but chronic illnesses like diabetes, arthritis, and arteriosclerosis — a fairly common problem associated with aging — can further damage the body and impact sexual function, McGough warned. For men, this most often results in erectile dysfunction and reduced libido. In women, these diseases can hasten changes to the vagina and make sexual activity more difficult. "Damage to the blood vessels that supply the clitoris and vaginal walls reduces the ability to produce lubrication," McGough said. "Thinning of the tissue in the vaginal walls [also] makes it more susceptible to tearing and irritation."

When in doubt, talk to your doctor about your symptoms and maintain open communication with your partner.

Let's talk about sex

Would you be surprised to learn that when it comes to sex, more isn't always better? In fact, a 2015 study published in Social Psychological and Personality Science found that having sex more than once a week doesn't translate to greater happiness, regardless of age, gender, or relationship longevity. So while sex might have a critical role in some people's lives, there's one universal takeaway: other than the non-negotiable presence of consent, there's no such thing as a "normal" sex life, whether we're talking about specific sex acts, or how frequently you actually have sex.

But like everything else in life, knowledge is power — so if you're looking to broach the topic of sex with your partner, the facts are a great place to start!