Bad dew and menstruation are quite different, they are different in nature, time of appearance, duration, traits, etc., and can be judged according to the details.1. Different nature: Bad dew is the necrotic ecchymotic tissue, blood, cervical mucus, etc., which flows out through the vagina during the recovery of the uterus after the delivery of the fetus. Menstruation is a physiological cycle, subject to the influence of ovarian cyclic changes, for the endometrium occurs in the cycle of shedding and bleeding; 2, the bleeding time is different: the bad dew appeared in 3-7 days after delivery, menstruation is in the normal menstrual cycle of bleeding. Menstruation occurs after the discharge of the evil discharge, and the earliest time is not more than 4 weeks after delivery; 3. Duration: the evil discharge lasts for 4-6 weeks, with a total amount of about 500 ml, and is usually completely discharged in 28-42 days after delivery. Menstruation usually lasts 2-8 days, and the bleeding volume is about 20-60ml; 4. Different traits: there are three stages of menstrual discharge, the earliest one is bloody discharge, followed by plasma discharge, and the last one is white discharge, the color of which gradually turns from bright red to white, while the normal menstrual blood is dark red and non-clotting blood.