There are many terms for the shedding of the uterus lining in female humans such as a period, catamenia, or the menses. The average period lasts between three to five days. However, like any continuous natural phenomenon, there is a degree of natural variation between results. Usually, the frequency of a continuous natural variable such as the length of a period is distributed normally around a peak that is the mean, median, and modal value. However, given that there is a cut off point of zero days, and that there are all sorts of other factors that might affect the length of the period, we might not expect a normal distribution curve for the graph of period length by frequency. As said before, the typical period lasts between three and five days. However there is a large amount of variability and it is not abnormal for a period to last anything between two days to one whole week. Of course, if someone has very regular cycles and all their periods seem to last exactly three days, then one abnormally long period of say a week may be more cause for concern. On the whole, the length that women experience menstrual bleeding does vary, and so the occasional outlying result should not be regarded as cause for concern.
There are many reasons why a woman might have an abnormally long period such as if they have taken a contraceptive pill, as this causes an imbalance in hormone levels. Diet, alcohol intake, and various other factors can change the behaviour of the menstrual cycles. For example, a study was conducted showing that even simply exposure to bright light in the mornings can alter the lengths of a cycle, and that moonlight does seem to have an effect on menstruation! Additionally, due to pheromones, women grouped together will tend to synchronise their cycles. With so many subtle and complex factors that can alter the length of a period, there is no exhaustive list of the causes for the length of a period to change, and chance variation does play a large part.
Having said that, if you experience a period lasting over nine days then it would be recommended that you see a doctor, as the lengthened period could be a symptom of internal damage. On the whole however, a period lasting seven days may easily just be due to chance, and unless this pattern continues, and beforehand long periods were a rare occurrence, there is probably nothing wrong. en.wikipedia.org/wiki/Menstrual_cycle was the primary source for this, and provides more information on this topic.
There are many reasons why a woman might have an abnormally long period such as if they have taken a contraceptive pill, as this causes an imbalance in hormone levels. Diet, alcohol intake, and various other factors can change the behaviour of the menstrual cycles. For example, a study was conducted showing that even simply exposure to bright light in the mornings can alter the lengths of a cycle, and that moonlight does seem to have an effect on menstruation! Additionally, due to pheromones, women grouped together will tend to synchronise their cycles. With so many subtle and complex factors that can alter the length of a period, there is no exhaustive list of the causes for the length of a period to change, and chance variation does play a large part.
Having said that, if you experience a period lasting over nine days then it would be recommended that you see a doctor, as the lengthened period could be a symptom of internal damage. On the whole however, a period lasting seven days may easily just be due to chance, and unless this pattern continues, and beforehand long periods were a rare occurrence, there is probably nothing wrong. en.wikipedia.org/wiki/Menstrual_cycle was the primary source for this, and provides more information on this topic.