Increased blood flow to the area can cause a woman’s breasts to swell to up to 25 percent larger than in their non-aroused state, which men should file away under extra incentives to take their time with the foreplay. Women’s breasts may also change in colour slightly, with redness or blotchiness appearing on the chest and the areolas and nipples darkening.

During the arousal process, the brain stem releases the pleasure chemicals like dopamine into your bloodstream. Once you start having an orgasm, however, the secreting stops and the full-on flooding begins. All sorts of happy hormones are released during climax, creating that blissful, euphoric feeling that keeps people coming back for more.

According to one study, sexually active people are healthier overall and take fewer sick days than their celibate co-workers. Intercourse also helps your body’s production of lymphocytes, which are a key part of the process of fighting off infections, and it increases immunoglobulin antibody levels which help your body ward off viruses, bacteria, and other invasive microbes.

During the early phases of the arousal process, the vagina begins “tenting,” which moves the vagina and the cervix closer together and helps create a suction that pulls sperm inward. Then, during orgasm, the muscular contractions that a woman experiences are, in part, the vagina further sucking inward, radically increasing the chances of sperm retention.

During intercourse, the body’s ability to tolerate pain increases dramatically, especially so among women. As women approach orgasm, their pain threshold is almost 100 percent higher than it is during non-sexy times. That’s because the areas of your brain that manage pain become highly active during sex and, for some reason, treat many sensations that would be classified as unpleasant under other circumstances as very pleasant indeed.

When you have an orgasm, one of the many chemicals released into your drug-addled brain is prolactin. Prolactin has a number of effects, including supporting the immune system, fighting cell death, and making you feel good. Prolactin also has the unique side effect of totally opening up the part of the brain that interprets smells.

During the arousal process, the glans and shaft of the clitoris fill with blood, making it stiffen and swell, sometimes up to double its non-aroused size. The clitoral hood also engorges, mostly to protect the highly sensitive clitoris from too much direct contact, and after orgasm, everything returns to normal within about 10 minutes.

From the moment you first get turned on all the way through your post-orgasmic bliss, the whole sexual cycle involves the circulatory system. Initially, when you just start getting aroused, your adrenal gland begins hitting your bloodstream with adrenaline, speeding up your heart and dilating your blood vessels. The sheer athletic endeavor of it all increases heart rate and blood pressure by 50 to 60 percent, thus increasing your temperature too.

This is crazy: Your vagina just doubled in size, had all sorts of blood flow and labia’s expanding, and then, during resolution, it all goes back to normal pretty quick. All of a sudden, it’s tight enough that it can keep a tampon from falling out. Even though it just fit a penis. It’s incredible. In fact, doctors say vagina’s are so elastic it just bounces right back after sex.

The increased blood flow during sex both eliminates toxins and gets more oxygen, which helps your dermis look younger, softer, and brighter. It also boosts collagen production, which helps stave off age spots and sagging. Sex can also be helpful to those that suffer from chronic acne because it can potentially regulate some of the hormone imbalances that cause acne in the first place.