Your birth control method
Birth control pills, patches, rings, shots, and IUDs aren’t guaranteed to stop your cycle entirely, but a missed period is a recognized side effect of hormonal birth control—one many women are quite happy about. This is because hormonal birth control methods are designed to both inhibit ovulation and thin the lining of the uterus, explains Alyssa Dweck, MD, ob-gyn and co-author of V is for Vagina: Your A to Z guide to Periods, Piercings, Pleasures and so much more. No egg to protect and no lining to shed means a lighter or non-existent period. The Mirena IUD and the Depo-Provera shot are the types most known for this side effect, along with pill packs, like Seasonique, that are designed for this express purpose. Learn more reasons you might want to switch from birth control pills to an IUD.
You’re exercising too much
The “female athlete triad” refers to a pattern of undereating, amenorrhea (loss of periods), and osteoporosis that stem from an extreme workout routine. But despite the word “athlete” in the name, you don’t have to be bound for the Olympics to be at risk. According to a recent study, it can affect women in any shape, form, or weight—not just the stereotypical “ballerina physique”—who are exercising too much. How much is too much? The answer is specific to each woman’s body and circumstances, but a good rule of thumb is if your workouts lead to a missed period, it’s too much for you. Check out these other 13 things most women don’t know about their vaginas.