I keep most makeup much longer
than the "rules" say to. I'm not a germaphobe, and I'm not tossing anything until it no longer pleases me to keep it. Or it smells funny.
mascara is a little different. My mom always harped on me to throw
away my mascaras after 30 days, and sometimes I did, and sometimes I
didn't. But, they definitely have a shelf-life - old mascaras are
teeming with bacteria, they dry out, get flaky or clumpy, and just look
bad. They are the one makeup product I will admit that needs to be
replaced on a regular basis - which is why a mascara subscription like
Bellimisa makes sense.