Donna DuBerg, SLU germ expert, talks about how germs hand out on those masks and why you shouldn't be sharing costume make up.
The chances of transmitting germs are quite high. Numerous bacteria were found including Staph.
For hard masks, DuBerg suggest soaking the entire mask in alcohol to kill the germs. You can also use Clorox wipes, but remember to also rinse those so there is no residue touching your face.