Angie
I don't know the cause, but I suffered from severe nosebleeds from about age 3. They removed my tonsils & adenoids (after which I hemorrhaged and had to be rushed back to the hospital). I am now 53, and our heat was very dry in those days, coal furnaces and we kept the heat high-no storm windows- At age 13 or so they stopped abruptly. Every once in a while over the years, I get what I remember as "the smell" which would precede the nosebleed. I was always healthy and even now my blood pressure is 100/70. So even though I do not have an answer for you, you might be able to deduce some similar info and solve this yourself. (That's how I solved my migraine problems--on my own-they are caused by foods-not the usual ones that everyone knows about. Best of Luck to you.