A period is when the lining of the uterus (womb) comes away and leaves the body through the vagina, a few days at a time. It happens on a repeating cycle, and for most people it starts somewhere in the early teenage years. This page is health information for learning, and a doctor or a trusted adult can help with anything that worries you.

The parts involved

The uterus (womb) is a small, hollow, muscular organ low down inside your belly, about the size of a pear. The ovaries sit either side of it and hold eggs. The vagina is the tube that runs from the uterus to the outside of the body. The vulva is the outside parts you can see, including the folds of skin and the small opening where the blood comes out.

The opening the blood comes out of is not the same one you pee from. There are two separate openings, plus the anus behind them. Knowing that in advance saves a lot of confusion.

If any word here is new, the glossary explains it plainly.

What actually happens

Each cycle, the lining of the uterus thickens. It is getting ready in case a pregnancy starts that month. Hormones — chemical messengers made in the body — control the whole thing.

If no pregnancy starts, the lining is not needed. It breaks down and leaves through the vagina over a few days. That is a period.

Then the cycle begins again. The gap from the first day of one period to the first day of the next is called the cycle length.

How much, and for how long

A period usually lasts somewhere between 2 and 7 days [NHS; ACOG].

The amount is much smaller than it looks. Across a whole period most people lose only about 2 to 3 tablespoons of blood in total [ACOG]. It looks like more because it is spread over days and mixes with the lining, which is why the colour can be bright red, dark red, brown, or almost black near the end. All of those are normal.

You may also see small clots, which look like little jelly-ish lumps. Small ones are ordinary.

What it feels like

Many people get cramping in the lower belly, a dull ache in the lower back, or both. Some feel tired, tearful, or more irritable in the days before. Some notice sore breasts, spots, or a change in appetite.

Some people feel almost nothing. That is normal too, and it does not mean your period is not "working".

Does it hurt to have one?

A period is not an injury and it should not be agony. Mild to moderate cramps that come and go, and that you can carry on around, are the usual picture.

Pain that stops you doing things is a different matter and is worth talking about — that is covered in is my period normal.

Will I know when it is coming?

Not the first time, and that catches almost everyone. The practical answer is to carry something with you in advance, which is what getting ready for your first period is for.

The first periods often come at odd intervals — a long gap, then a short one — and that settles over the first couple of years [ACOG].

When to see a doctor

Nothing here needs a doctor by itself. You or a trusted adult can arrange to see one if:

• you have not had a period by about 15
• your breasts started developing about three years ago and no period has come
• bleeding soaks through a pad or tampon every hour or two
• pain stops you going to school or doing your usual things
• you are bleeding between periods, or after sex

None of those means something bad has happened. They are simply the things a doctor would rather look at than not, and it is fine to ask an adult to help you arrange it. You can also read about what else is changing while you wait.