The colour of the blood changes during a period. The period contains most blood on the days when you bleed most heavily, often the first two or three days, so it is redder than at the end of your period, when the blood is more mixed with the mucous naturally present in your uterus and which the body is flushing out. At this stage, the flow is often slightly brownish. Some girls have brown-coloured flows at the start of their periods too. When you bleed less, the blood has time to become brownish in colour on its way out through the vagina. The blood can also turn brown in your sanitary towel. Find out more about periods. Read our article entitled “Periods – a basic course.”