What is Living on Robyn’s Makeup Brushes: A Horror Story

Let me start this post by saying: wash your brushes, you dirty hippie. Not only does the process of cleaning makeup brushes remove old, crusty makeup, dirt, oil, and dead skin cells, it helps to remove festering bacteria.

I take pretty decent care of my brushes. I wash them once a week, and I spray them with Sephora’s anti-bacterial daily brush cleaner after each use. I decided that I wanted to see what effect brush cleaning had on the bacteria diversity living on my brushes.

For this investigation, I used my Tarte Airbrush Finish Bamboo Foundation Brush, which is my favorite everyday foundation brush.

Now that I have posted the nail applique comparison, you guys can all see how long I have been procrastinating on certain posts…

To wash the brush, I used the Sephora brand makeup brush shampoo.

Using a q-tip, I exposed one Petri dish filled with an agar growth medium to the bacteria living on my unwashed brush. Then, I washed the brush and exposed a second plate to its cleaner state.

As a note, since this would be really easy for you to replicate at home: make sure that if you try this that you do NOT directly touch the brush to the agar. Otherwise, you would create a bacterial paradise on your brush!

Then, I waited for two weeks, ready to check out my fascinating colonies:

The “before” petri dish.
The “after” petri dish.

I will admit, at first I was a bit disappointed about a perceived lack of improvement between my “before” and “after” cultures. However, closer examination revealed that the difference was more noteworthy than it initially appears. That fuzzy mold obscures the truth! The “before” culture had what looks like about ten distinct species, whereas the “after” culture had a mere five.
Furthermore, it is worth noting that the fact that I consistently wash my brushes likely decreases the effect. Someone who hasn’t washed their brushes in two months would likely see a much more dramatic decreased in bacterial diversity and species concentration.

So, what is living on my makeup brushes?

I used a dissecting scope to help me characterize the colonies more accurately.

Without some relatively time-consuming tests, it’s hard to identify the precise bacteria that I found growing on my beloved brushes. However, I can make some educated guesses.

The fuzzy white stuff is, as I already noted, clearly some sort of mold, although I am not certain what species it is. The yellow colonies look suspiciously like Micrococcus luteus, a Gram-positive bacteria that typically lives in dust, soil, and on human skin. There also seems to be a few colonies from the genera Bacillus and Colstridium, although, again, I am not certain about the species. Other likely culprits include Staphylococcus and Streptococcus.

Although all of these bacterial species would normally be present on your face in small quantities, the opportunistic bacteria that thrive on makeup brushes should not be continuously re-introduced to your face, lest they aggravate acne and other skin conditions. So, again: go wash your brushes. The internet will still be here when you get back.


  1. Carolina

    “The internet will still be here when you get back.”
    LOL A+ would read again.

  2. Amanda

    WELL, now I’m just horrified to think about how long it’s been since I’ve washed my brushes. I try to wash my foundation brush once a week, but I think I’ve only ever washed my blush brush and other sundry brushes once or twice since I’ve had them. Yikes! I’m surprised there isn’t furry white mold growing on my cheeks.

  3. hellocampcomfort.com

    Do the others at the same time! Or at least have ones you can sub out for if you’re feeling lazy…

  4. penthesileia

    You just gave me a way to justify buying new makeup brushes, thank you (lol)

  5. Jasmine (TheHappySloths)

    Maybe because I am in bio major and taken a few labs and everything, but this doesn’t really surprise or irk me, every single surface on our home and our body is pretty much infested with bacteria. With that said, I’m washing my brushes tomorrow 😉

  6. whateveramber

    Um, ew. I’m a total goober and only wash my brushes about once a month or so. (In all honesty, I only wear makeup 2-3 times a week.) I use my fingers for my liquid foundation, so my brushes are only used for finishing powder, blush, and eyeshadow. I can’t imagine that would make much of a difference in the bacteria types and such living in the brushes, though.

  7. penthesileia

    I do the same thing – infrequent washing, but I only wear makeup 1-3 times a week and more often it is just once or twice (an outing with friends, for example). I feel like I’d wash them more frequently if I had a regular schedule, but alas, a grad student am I.

  8. LabMuffin

    I’m a bit of a grub (I have hay fever and was doing antibiotic research, so I’m pro throw-your-kids-in-mud and anti disinfect-all-the-things), so I may bit quite biased – but doesn’t this just say qualitatively what sorts of bacteria you have on your clean/unclean brush, and not quantitatively how much, which I think is more relevant to the ick factor and likelihood of causing skin issues?

  9. LabMuffin

    (Never having done any proper microbiology, I actually have no idea how one would go about quantifying bacteria on a makeup brush…)

  10. hellocampcomfort.com

    That is correct. That’s why I looked at number of species as a relevant factor, instead of just “amount of ick”.

  11. OMG!
    I really love your post! That’s why I lke to deep cleaning after one or two uses of foundations!

  12. jornakat

    this is SO COOL. i’m a new reader but i love everything i’ve read so far!! brb going to wash my brushes.

  13. penthesileia

    Yeesh, I need to go wash my makeup brushes.

  14. chicdabbling

    Very enlightening. One question, it looks like you are using a liquid/cream foundation? does this bacteria experiment hold true for powders?

  15. All is fair in war.