Brown period blood is usually caused by older blood that takes longer to leave the uterus and darkens when exposed to oxygen. If you wonder why is my period blood brown, common reasons include light menstrual flow, the beginning or end of your period, and hormonal changes. However, persistent brown bleeding with severe pain, unusual odor, or heavy bleeding may require medical attention. USA Fibroid Centers helps women understand menstrual changes and explore treatment options for uterine fibroids and related symptoms.
https://www.usafibroidcenters.com/blog/why-is-my-period-blood-brown/