A Beauty Blender Disaster!

So a few months ago in my Birchbox, I received a Beauty Blender. I fell in love with how the sponge blended in my under eye concealer without it caking. I washed it religiously after I had used it, and would leave it to air dry. A few months after owning the sponge, I noticed a few black dots, and I thought this was some mascara from my lashes that had landed on it after applying extra concealer.

I was so wrong. I carried on using the Beauty Blender thinking it was just mascara dots that I couldn't wash out. I started to notice that these dots were spreading around the blender, and I knew for a fact that these weren't mascara dots (I stopped applying more concealer after I applied mascara).

I did a Google search and I saw a lot of other people had the same problems. A YouTube video showed me one beauty guru's Beauty Blender was covered in mold, but she'd left hers in a plastic bag. Some people left their beauty blenders to dry in their make-up bags. But mine was left to air dry, so how did I get mold?

I honestly do not understand how it's happened!
Do you own a Beauty Blender or plan to own one? Have you had this happen to your blender?

Jenny xo