Certain types of hormonal birth control can cause a lighter flow, as can hormone imbalances involving the thyroid or pituitary glands. Rare medical conditions like a Mullerian anomaly (a malformed uterus) or an imperforate hymen can also inhibit blood flow, according to CNN. Menopause, pregnancy or excessive exercise can also cause a woman’s period to slow or stop.
According to one CNN, a light period is one that requires only a light panty liner or light pad. Progestin-only or low-dose combination hormonal birth control pills can cause a lighter flow, as can the intrauterine device (IUD) hormonal birth control method. Some women who use an IUD eventually stop getting their period altogether, according to WebMD.
For women of a reproductive age, a light period could be an early sign of pregnancy. Some women experience light bleeding during pregnancy, while others mistake spotting – a common early sign of pregnancy – with a light flow. For women in their 40s or 50s, a light period could be a symptom of perimenopause, a period of slowed estrogen production that takes place prior to menopause.
Excessive exercise can also lead to light or even absent periods. According to WebMD, anywhere from 5 to 25 percent of female athletes stop getting their periods due to excessive amounts of physical activity. This is termed exercise-induced amenorrhea, and is especially common among runners and ballet dancers.