If there is always a smell of urine in your underwear, the following causes must be ruled out: 1. caused by vesicovaginal fistula, because there is a loophole between the bladder and the vagina causing urine to be discharged from the vagina, this situation not only has a smell of urine in your underwear, but also often feel wet underwear, it is recommended to do a gynecological examination, if necessary, a cystogram can be diagnosed; 2. caused by certain diseases, for example, when there is bacterial vaginosis, the vaginal discharge is more, and the color is yellow, thin, the most important feature is that the discharge has a relatively large fishy odor, a routine laboratory test of the white belt can be clearly diagnosed.