Natural body chemicals, or hormones, cause your ovaries to release one egg about once a month. Most months, the egg and the lining of your uterus come out of your vagina as your period.

What comes out during your period is the blood and tissue that build up as the lining of your uteruseach month.Your period flow can be light, heavy, or in between. Sometimes menstrual blood also will be different shades of red, from light to dark. You may see some dark clumps or clots of blood, which is normal.

Your period may be heavy the first day or so each time and then decrease on later days.
Periods usually last between three and five days. It is normal to have periods that are shorter or longer, up to seven days. It is also normal if your periods are not the same number of days each month, especially in the first years.