Could it be harmful if you have your first period and you don't have a tampon or a pad on?

?? no: But it may be messy, if your period is too long or too heavy see your obgyn.

Not harmful: If you are getting close to that age you might want to carry a pad in your book bag or purse. The only significant problem might be embarrassment if the bleeding flows through clothing. Check this site: http://www.Youngwomenshealth.Org/tampon.Html.