Do Cats Get Periods (Menstruation)?

1 Overview

Why is that?

Because cats are special: they ovulate only after mating during estrus, but mating does not guarantee fertilization. If fertilization fails, the eggs are destroyed by white blood cells rather than expelled, as in humans.

So the difference between cat and human cycles is:

Humans mature and release one follicle each month, alternating sides. During ovulation the body prepares ample nutrients to receive sperm and await new life.

If no pregnancy occurs, the excess nutrients under estrogen and progesterone cause the uterine lining to shed every 28–30 days as menstruation, flowing out.

Cats have estrus, but ovulation occurs only when stimulated by mating; without pregnancy, no menstrual shedding occurs.

The feline estrous cycle

Would humans envy cats, then?

Although cats avoid the trouble of periods, estrus is far more painful than for human women!

During estrus, under hormonal control, cats become unusually restless and unable to restrain themselves, focused only on finding a male—with calling, poor appetite, raised hindquarters, and inappropriate urination.

A female’s estrus begins in spring as days lengthen and stops as it cools. Each lasts about 7–14 days, and if no pregnancy, it starts again after 14–21 days.

The frequency is very high—more than menstruation—and repeated estrus without pregnancy greatly raises the risk of pyometra.

This is because the ovaries secrete large amounts of progesterone, which triggers endometrial growth and secretion, so fluid accumulates in the uterus and it enlarges; over time more fluid builds, and once bacteria enter, they multiply and form pus.

Early pyometra shows few signs and is hard to notice. Over time the cat changes—reduced appetite, swollen belly, frequent licking of the vulva; in mid-to-late stages the belly clearly enlarges.

Pyometra has two forms: open and closed.

Open pyometra:

The vagina continuously discharges pus or pus-blood, which the cat often licks away, making it hard to notice.

Closed pyometra:

No vaginal discharge, but the cat still licks often.

In late pyometra, the cat shows fever, anorexia, vomiting, weakness, and weight loss.

Pyometra is life-threatening because it causes severe anemia; without prompt treatment the cat can die quickly.

The best solution for estrus and pyometra: spay the female cat!

In summary: female cats do NOT menstruate! So if you see vaginal bleeding, it is usually disease-related—take the cat to the vet right away!