Whether you’ve had your first period or are about to have your 200th period, you may be wondering, “Can sex kick-start your period?” After all, there is evidence that sex can have a range of effects, from blocking pain to improving mood and lowering stress (1; 2). Maybe you’ve even gotten your period right after having sex—which could be a good or bad thing. (On one hand, maybe it’s a relief. On the other, periods can suck.) So, what’s the deal? Can sex make your period come sooner than expected? What’s the connection between sex and the menstrual cycle? Are there other reasons you might experience bleeding outside of your period?

Can sex kick-start your period? 

Experts agree, having sex will not kick-start a period. The drop in progesterone levels at the end of the menstrual cycle triggers the beginning of the period; there’s no other way to start it (3). But, if your period is coming up, having sex may help some period blood exit the body sooner than it would have without sex. 

If you’re about to get your period, but haven’t started to bleed yet, and you have sex and climax, it’s possible for the uterine contractions experienced during orgasm to facilitate or expedite the initial light flow (4). The same thing can happen when you believe your flow is over—an orgasm can cause uterine contractions that release residual blood.

To understand exactly how sex can make your period seem like it’s starting sooner, first you need to know exactly how the uterine lining (called the endometrium) changes throughout the menstrual cycle. Starting with the last day of your period, when bleeding is complete, the endometrium is a thin layer of cells. As the cycle enters the proliferative phase, the endometrium thickens thanks to rising estradiol (a reproductive hormone that influences the menstrual cycle). This is the time during which the endometrium is growing to support a pregnancy if one occurs (3).

Ovulation occurs next, and usually an egg is released from the ovaries. During this phase, glands in the endometrium rearrange to provide nutrients to the uterus that can help keep a pregnancy healthy. Following ovulation, the secretory phase will occur if there is no pregnancy. In cases where there’s no pregnancy, two reproductive hormones called estradiol and progesterone encourage the uterine lining to break down. The endometrium also secretes prostaglandins that tell the uterus to cramp. This results in the endometrium being sloughed off as menses begins (3).

If you are about to menstruate, sex can make period blood exit the body sooner because orgasm causes uterine contractions that are similar to the natural uterine contractions caused by prostaglandins (5).

When we posted the question “Has having sex ever made your period come early?” on Twitter and Instagram, we got several responses from those who say that sex has made their period come early. 

“Okay, so sex always affects my period,” Krystal P. tells O.school. “It'll make it happen early since orgasms tend to jumpstart your cycle. If I'm in a consistent relationship, my period changes during that time.” Another anonymous responder seconds this, explaining, “My periods are already irregular, since I have endometriosis and ovarian cysts. Sometimes if I do have sex, I can bet my period will come for a few days or be a full-blown period. I don’t know if they’re related, but that’s just what happens.”

Kellie K. says that the same has happened to her, stating, “Yes, it has—particularly if I have penetrative sex within one to two days of when it is supposed to start. In fact, times that it’s been a few days late, or I’ve wanted it to start a bit early, penetrative sex has been a nice way to give a little ‘Hello!’ to my uterus, though it certainly doesn’t work every time. Alternatively, if I have penetrative sex too soon after my period has ended, it can sometimes cause bleeding to start again.”

Another user was even experiencing this when answering our Instagram query. “Had sex last night and got my period today. Four days early,” writes @keytomore. 

What about your very first period? Can having sex before cause you to menstruate earlier? 

Again, the answer is no. Having sex will not change the timing of menarche (a person’s first menstrual period (6).

It’s important to know that pre-menarche sex can still lead to pregnancy and the transmission of STIs. Anyone thinking about having sex should seek out a healthcare provider to discuss birth control options; Planned Parenthood is an excellent choice. If you cannot see a provider, and want to have sex, make sure to use a condom or other form of protection to help prevent unplanned pregnancy and STI transmission (6).

What else can cause you to bleed after sex

Bleeding after sex—which can be mistaken for an irregular menstrual cycle, and vice versa—can be a sign of:

• Vaginal dryness
• An imbalance in the vaginal flora
• STIs like gonorrhea or chlamydia
• A tear in the hymen
• A growth in the vagina or cervix, such as a benign polyp, fibroid, or very rarely, cancer
• A precancerous abnormality on the cervix (this is typically picked up on pap smear)

The most serious, but least common, causes of bleeding after sex are cervical cancer and uterine cancer. Although those who experience bleeding after sex are very unlikely to have these cancers, if you notice vaginal bleeding unrelated to menstruation, you should visit your healthcare provider as soon as possible for proper diagnosis and treatment (6).

So while sex can’t exactly cause your period to come early, it can make it visible sooner. If you experience bleeding after sex and aren’t sure what’s going on, contact your healthcare provider.