My friend's last period is july27,she's having a viginal spotting/bleeding since yesterday.what maybe the reason of this?is it critical?pls.help.

Depends: It depends on a couple of things, but most importantly, has she had unprotected sex and is she able to get pregnant? If so, check a pregnancy test. If negative, it can still be positive later. She could also have gotten something else besides pg (STD's). If there is zero chance of pregnancy then there are other causes. Often it is nothing. If there is pain, fever, or dizziness, to ER.