[2D Platformer] How do i make a platform that is only active when the player is standing on it?

Hi,

Im trying to make a platform that won't interact with anything unless a player or object is touching the top of it. i have added a box collider to the platform but it gets quite annoying when i jump under the platform and my player bumps into it. i would like a solution in which my player can jump through the platform without interatcting with it untill it touches the top of it.

Thanks

:D