eyelashes thinning for no apparent reason

okay, i was born with some long and thick eyelashes, but recently my eyelashes have become so thin that theyre see-through. im young and i dont use mascara, so i have no clue why theyre thinning. I rarely ever curl my eyelashes either.

any ideas on what could be the cause? whenever i look it up it just tells me that it comes with old age but im not old!!