It's quite normal for the old, but it's rare while in the young days. Eyelashes, which is is part of the hair of human body, get their color from the pigmentation which is called melanin. They are existing in our hair follicles. When melanin in hair follicle is depleted, the eyelashes will turn grey to some extents. There are many different reasons give rise to this result, including the result from natural, medical impact or genetic disorder. Aging is the leading and most common cause of grey hair. For people who are over 40, they begin to grow lighter colored hair and gradually grey finally. But it takes longer for eyelashes to lose its color, so grey eyelashes are not very common appearance for people except over 70. Thus, if you have this symptom, you may suffer some disease, such as extreme mineral substance deficiency, or other wired problems. In consideration of your health, you'd better see a doctor as soon as possible.