The blood on the fourth day of menstruation is brown, generally do not worry too much, this situation is a normal physiological reaction. The blood is usually dark red during menstruation and may slowly and gradually decrease around the third day. The brown discharge at this time is caused by the problem of the late menstrual flow decreasing and the presence of menstrual blood in the body for too long, which can generally be treated without the need for treatment. However, you must be careful to judge your own body condition, not all brown menstrual problems are normal. The brown menstruation may also be caused by gynecological inflammation or infection, or it may be caused by coldness or lack of qi and blood that needs to be adjusted and improved.