Not All Pits Are Equal

Yesterday, Dr. Julie Horvath introduced you to our Armpit Microbe Pilot Study, known as #PitStart to those of you following along in real time on Twitter. Before we start asking thousands of you to send in smelly Q-tip’s that you’ve twirled around in your armpit, we need to work out a few methods. Namely, we’re concerned that some deodorants and antiperspirants inhibit bacterial growth – this was Julie’s personal experience when she tried to plate out her armpit microbes a few months ago.

So Dr. Julie H. and Dr. Jul Urban, the Assistant Director of the Genomics & Microbiology Research Lab at the Nature Research Center (NRC) at the NC Museum of Natural Sciences, and their trusty lab interns recruited 18 people, 9 men and 9 women, to go without deodorant or antiperspirant for a week. Full disclosure: I’m a participant.

On Sunday, participants went about their normal personal hygiene routines, applying deodorant or antiperspirant as per usual. Yesterday, we started the ‘Au Naturel’ treatment and will continue to go without deodorant/antiperspirant for the rest of the week. Every day between 11a and 1p, we have to sample each armpit with a sterile swab. Protocol calls for you to twirl the dual-tipped swabs in the deepest, wettest part of the armpit for 45 seconds. That’s longer than you think – Ok, at the risk of sharing too much information, here’s another disclosure: I take my phone in the bathroom with me and use the stopwatch app to time myself while swabbing. 45 seconds is an unbelievably long time.

Each day participants then deliver the day’s swabs directly to the Genomics & Microbio Lab at the NRC. There, members of Team Armpit dip and vigorously twirl a tip from each swab in a vial of liquid buffer to shake off the microbes. They then use a pipette to suck up a small volume of that microbe-laden liquid and spread it across a plate filled with nutrient-rich agar. The plates are plopped into a 37 degrees Celsius (or 99 degrees Fahrenheit, aka body temperature) incubator for about 24 hours, and we wait for the bacterial colonies to grow (or not).

Today, when I delivered my samples to the NRC, I had a chance to take a peek at the armpit microbes I collected on Day 0 of the experiment (the last day I wore antiperspirant).

Lucky for you, I brought my audio recorder with me. Here I am talking with Dr. Jul Urban:

Did you catch that? For Day 0, the plate from my right armpit barely had any bacterial colonies growing. Yet for the same day, the plate from my left armpit was FULL of bacteria!  I took some pictures so you can see for yourself.

Clearly there is more microbial action going on in my left armpit than in my right!

As you heard in the audio, Julie hypothesized that the difference may be due to sampling effort. Perhaps because I am right-handed I swabbed my left pit more vigorously as I was using my dominant hand to do so. Yet, I think I’m meticulously and vigorously sampling both pits with equal effort (Hello? I use a stopwatch to time myself).

I checked back in with Julie later this afternoon, and she reported that I am not the only one showing this differential growth in each pit. Apparently there were quite a few other folks whose plates from Day 0 (Normal Habits) showed a similar pattern.

Chatting these findings over with a few friends and colleagues, I learned that many people have observed one pit regularly being more sweaty and smelly than the other. Is this the case with me? Does that explain the freak-show growth of microbes in the left armpit and not in the right? I must admit that I’ve not really noticed this about my body before, but perhaps now I’ll start paying more careful attention, particularly since I’m going without antiperspirant all week and will be extra smelly.

As #PitStart is an experiment in real-time, we’d love to hear your thoughts, hypotheses and observations about your own armpits. Drop a comment on the blog or participate in the conversation on Twitter (#PitStart).

By | 2016-11-22T13:47:33+00:00 August 28th, 2012|

About the Author:

Holly Menninger
As Director of Public Science, Holly coordinates our empire of citizen science projects and manages the online science communication here at Your Wild Life. An entomologist by training, she’s a science communicator by passion and practice.

19 Comments

  1. loveswildlife August 29, 2012 at 10:59 am - Reply

    i’m glad you brought this up. my friends and i are always talking about how one pit seems sweatier than the next. can’t wait to see what you find out about this . . . maybe right guard would be interested! keep us posted!

  2. Daniel C. November 15, 2012 at 2:36 am - Reply

    I’d like to put forth my idea that the amount of sweat in each pit is effected by one’s handedness. The arm yo0u use less stays close to your body giving the sweat less chance to evaporate and the pit stays warmer.
    The arm you use more has a greater amount of activities that move it away from the body and fan or “air out” the underarm. That pit should on average should be have a lower temperature.

    • edward August 13, 2016 at 4:24 pm - Reply

      I also was wondering why my left arm pit smells worse than the right when I sweat I just started to notice it, but after reading some of the comments it makes sense to me that if you are right handed you use your rt. arm more than the left allowing more air to circulate through your rt arm pit causing it to stay dryer than the left that is kept closer to the body trapping in sweat & heat & therefore not evaporating causing the sweat odor more so that the left & vice a versa if you are left handed. I have read comments that the arm you use the most would have more odor but that’s not true since I am rt. hand & my left arm pit has the odor.

  3. Lee O'Doud December 12, 2012 at 9:55 am - Reply

    I have never used deodorant in my life, reason being no odor whatsoever. However my sister has a big problem with odor. Reason being??????

    • Brian L. October 8, 2015 at 10:12 am - Reply

      I wonder if the reason has to do with diet? Do you eat a healthier diet than your sister?

  4. Sho January 18, 2013 at 2:43 pm - Reply

    Today I (f, 56 year old) go out without feeling stressed. Years before I felt different because I usually smelled very bad on my right side (right armpit). Even when I washed myself before leaving home, 2 hours later the smell was back but never on my left side!
    Believe me, I hated people saying “clean people do not smell…”

    • Merijn April 2, 2013 at 3:43 pm - Reply

      How did you manage to solve your problem? I too have rather smelly pits, long time it was only the right one, now they worsened both. I know about the ignorance, hate people who don’t have this problem thinking I’m not hygienic, it’s not the truth.

  5. cherie April 14, 2013 at 5:46 am - Reply

    Merijn: in another one of these posts, someone said they stopped using antiperspirant and began to rub their arm pits with alcohol after his or her daily shower and they no longer have any odor. Thr bacteria is what smells, not us. P.s this person lives in Florida. I am going to try this. It decreases aluminum on our body which is a good thing. Antiperspirant usually contains aluminum.

  6. Val June 28, 2013 at 9:33 pm - Reply

    Is it possible that the right handed person, might be moving their arm right arm away from their body more often during the course of the day, thereby giving the right underarm an occasional airing / drying out…….which the left side underarm wouldn’t be receiving? Just food for thought.

  7. Len July 10, 2014 at 4:48 pm - Reply

    I broke my left arm 3 months ago. Before that I had very little armpit odor, regardless of deodorant used. Since then, starting immediately after the break, I have had terrible pit smell on that arm. The arm is mostly healed now (still a little muscle pain) and the odor has not abated. Right pit is always fine, but even if I wash the left one several times a day it quickly gets smelly again. I’m guessing the trauma caused the problem but wondering if anyone else has had this problem and whether it eventually abated.

  8. Elaine Baird November 7, 2014 at 9:09 am - Reply

    I have been suffering from stinky left armpit for a few years. I researched homemade deodorant recipes. Although I haven’t actually made my own, a few months ago I started applying coconut oil to my armpit and switched to non aluminum deodorant. Instantly I noticed no odor at all. I am now no longer worried about how I smell and no longer need to apply deodorant throughout the day. Research coconut oil. Its amazing. I buy the coconut oil near t by e Crisco section. Not the liquid oil. I thought my armpit would feel greasy throughout the day. But it does not.

  9. Kim November 11, 2014 at 11:39 am - Reply

    I found this because I was curious if anyone knew why my left pit smells when the right does not. I’m right handed so the airing out theory is probably the reason for me. It does not bother me too much as I am using a beautiful all natural deo with coconut oil and arrowroot powder made by Refyll. Google it and get some or make your own with these things because it absorbs moisture as well as keeps bacteria in check. I would make it but refyll’s is cheap and I just don’t want arrowroot powder flying all over my own kitchen. lol

  10. meri December 8, 2014 at 10:18 am - Reply

    I stopped using deodorant and for 2 weeks used apple cider vinegar to open and clean out the glands. After those two weeks I have not had odor at all. I do sweat. But it does not smell. I just put the apple cider vinegar in a small spray bottle and used it morning and night. I did this in the dead of summer. I repeat it periodically. But have had great success.

  11. Dana June 23, 2015 at 9:18 pm - Reply

    Have had this problem for the last few years. My hypothesis as to the cause of one pit being worse is thus- In anatomy class I learned that our glands which process toxins work on left and right sides differently. ( Forgive me, I have memory problems and at this time can’t recall the technical names for these glands) Anyway, I believe, through our sweating out of these toxins from our armpits, that it is possible bacteria are more attracted to or more prone to congregate and propegate in the armpit that releases more of said toxins.
    Basically what I’m saying is- We sweat out toxins, possibly more on one side of our bodies, bacteria like one side more than the other because of this. Thus one pit smells worse.
    Does that make sense to anyone but me?

    • Dave August 16, 2015 at 8:55 pm - Reply

      Dana, it DOES makes sense! Your skin does indeed help to flush out some of the toxins in your body and and your armpits can do this unevenly.

      I read another article that explained that if the right pit smells more, it’s because your liver is on the right side of your body and is probably over taxed with toxins. A smelly right armpit can be a good sign of liver problems. It is recommended to do a liver cleansing diet, to clear up the problem. Most of us eat diets that are too fatty for us and the glands in our armpits can start receiving too many fatty acids, that change the bacterial composition of our sweat glands. So, a change in diet will actually help this problem.

  12. Vicky October 6, 2015 at 4:57 am - Reply

    For anyone looking for something non-aluminum based, I would recommend Lavilin. It is amazing!

  13. John April 19, 2016 at 11:18 pm - Reply

    Here’s an idea. When you put on deodorant, do you always do it in the same order? The bacteria from your pit will be on the deodorant after use. There, it could possibly grow and the next time you apply it to that same arm, you’re putting more bacteria infested stuff on the first one you apply it to. Most people are righty, so the left one is the first to get the stuff. :)

    • Wayne September 12, 2016 at 10:04 am - Reply

      Interesting theory, but I doubt that’s the case. I rarely use deodorant, and occasionally will abstain from showering for several consecutive days. My left armpit has a significantly stronger scent than my right one, but the moisture levels appears to be consistent between the two.

  14. Wayne September 12, 2016 at 9:54 am - Reply

    The Internet is an amazing thing! All my life I’ve been intrigued that my left armpit has far more of a scent than my right one. I only wear deodorant when I have to out of respect for others, but I prefer not to because I don’t think it’s natural and I dislike the way it makes my pits feel. Perhaps TMI, but I love the scent of sweat, and I don’t even really understand why… I just do!

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