Falling eyebrows: alopecia or not? I have been losing my eyebrows now for 4 years.

Hi! they fall and grow back. Sometimes they fall from same place and sometimes just thinning everywhere. They don't fall without pulling them gently when they itches very bad and then they always fall! My dermatologist doesn't know what it is.I don't have any baldness on scalp. The hair that falls out are light colour from the root and dark from ends which should be the opposite. I'm worried if the eyebrow hairs are dead and fall totally! Thank you!