Bathroom Steam Shower Why Does The Mirror In My Bathroom Steam Up When I Take A Shower Some Days And Not Others?

Why does the mirror in my bathroom steam up when I take a shower some days and not others? - bathroom steam shower

I know nothing about science ........ He immediately went to school, and the world will no longer be broadcast tomorrow on BBC 1 a few years ago I just blindly trust that the things! PS useful background information - I have no hood, and often myslelf razor cut due to a tarnished mirror!