In fact, most were only seen on a single individual. Despite the staggering diversity, the vast majority of bacteria found in human navels come from but a handful of species. Together, those eight species accounted for almost half of all bacteria found. The researchers also found three species of archaea, a type typically found only in extreme environments. Interestingly, two of the three came from a single individual who said he hadn't taken a shower or bath for several years.
Even if you shower every day, lint still collects Credit: Getty Images. Why so much belly button biodiversity? They draw an analogy to fish within an estuary. The permanent residents have adapted to the estuarine habitat, while other species that may briefly show up just aren't equipped to take up long-term residence.
Likewise, a disproportionate number of trees in any given rainforest are uniquely adapted to the tropics. Others may be able to grow in rainforest soil, but they can't establish a strong community. While the sheer diversity makes it impossible to predict which types of bacteria might be found inside any individual human's belly button, what the researchers can do is predict which species are most frequent and which are rarer.
So if your belly button doesn't routinely snag lint to form a ball of fuzzy fluff, fret not: your navel is still an exciting place. Truly, it teems with life. Body Matters Bacteria. Sometimes people find a fuzzy little ball of fibers in their navel.
Some refer to this as belly button lint, while others call it belly button fluff, navel lint, or navel fluff. According to the Canadian Medical Association Journal, research in concluded that belly button lint is a combination of body hair, skin cells, and clothing fibers.
And your belly button typically has an odor for one of two reasons: hygiene or infection. In a study at North Carolina State University, researchers found that almost 70 different types of bacteria reside in the average belly button.
Along with an odor, a bacterial infection might also include a brownish or yellowish discharge. Your doctor will most likely recommend that you keep your belly button clean and dry and might prescribe antibiotics such as:. Your belly button provides an excellent damp, dark environment for a type of yeast called Candida that can cause a yeast infection known as candidiasis.
Candidiasis can result in a red, itchy rash along with a white discharge. There will most likely be an unpleasant smell, too. Your doctor may recommend that you keep your navel clean and dry and apply antifungal cream such as:. Belly button lint is common and harmless. Cross-sectional view represented by the circle of the lint showing the different forces acting on it.
Note that since the fabric is moving rightward, the frictional force exerted by the lint on the fabric will be leftward. Assuming that the lint is also under the same amount of pressure, the normal force transmitted to the lint fiber from the shirt is given by. If we idealize the lint-fabric system as a cylinder in contact with a flat surface as in Fig. However, in practice, the roughness on the surfaces and localized solid deformation at the contact points will result in a finite real area of contact.
Accurate determination of the real contact area remains a major challenge in tribological calculations As explained earlier, this is attributed to the fact that the cuticle layers are aligned in the root-to-tip direction; hence the friction is weaker in that direction. Consequently, as per Eq. Assuming that the inhale and exhale phase are of the same duration, the average velocity of a lint fiber in a breathing cycle is then given by. We remark that the sliding motion between two dry surfaces can exhibit very rich and complicated dynamical features such as stick-slip and chaotic behavior 12 , which are disregarded in this simple model.
Further, we neglect other possible secondary events that are likely to occur during sliding such as elastic deformation of the fiber, its rotational movement, and any change in its orientation with respect to hairs.
Even though the weight of a lint fiber is comparable to the garment pressure force, we do not include gravity in the above force balance due to the following reasons. The results from the survey conducted by Dr Karl Kruszelnicki 1 strongly suggest that the lint can migrate in a direction opposite to that of gravity and thus it plays little role in lint transport to the navel.
To obtain a numerical estimate for the average velocity, we consider the shirt material to be cotton. Coefficient of friction between cotton and human hair, is reported to be approximately 0.
From a visual inspection of the individual fibers from BBL, it is apparent that they can be a few millimeters long. The numerical values of the parameters used are summarized in Table 1. Next, let us consider the equation governing the evolution of concentration of lint fibers on the body at a given time and space. As noted earlier, for simplicity, we focus only on the motion of lint fibers along one direction say, along the midline connecting the navel to the middle of the chest , allowing a one-dimensional approach.
The generalization to two dimensions, e. The coordinate system used is shown in Fig. A simple mass conservation of the lint fibers leads to see Supplementary Material for derivation. These assumptions are justified because the contact conditions between the skin and the shirt which dictates both the sliding velocity and production of lint fibers are not expected to change drastically over a short distance from the navel.
With these assumptions, Eq. The second term on the right hand side of this equation is the complimentary function of Eq. Illustration of spatiotemporal evolution of the second term on the right hand side of Eq. An arbitrary initial distribution is shown by the solid red curve. Given this solution, we can now calculate the influx of lint fiber to the navel. Using Eq. Note that the second term on the right hand side of Eq.
With reference to Fig. We consider the asymptotic behaviour of the solution given by Eqs 13 and 14 at very small times and at large times. Further, we can assume that the estimate of the initial distribution is reasonably close to a constant, i.
Thus, we have. Consequently, we get. This is corroborated by the previously made observations 1 , 2 that the color of BBL matches the shirt that is worn. In other words, the lint fibers constituting the BBL mostly originate from the shirt worn, or, the source term is the major contributing factor for BBL production. The experimental data available from Steinhauser 2 is from the specimens that he collected at the end of the day.
At such large times, we expect that Eq. For example, a tighter shirt would imply higher probability of lint fibers getting dislodged from the cloth. Also the one-dimensional model considers the lint fibers coming into the navel from just one direction. For completeness, we now look at the short-time limit, where the second linear term is important; thus. Then Eq. To further corroborate the validity of our model, we now provide more qualitative arguments showing how the model is consistent with a variety of experimental observations previously made 1 , 2.
For instance, it is reported that aged and more physically active individuals show more propensity to produce BBL. Since, as per our model, breathing is the driving force for the production of BBL, the increase in respiratory rate with age 15 and physical activity explains this observation. The model also reveals the reasons for the observation that larger bellies accumulate more BBL. In passing, we comment that breathing-induced transport of lint fibers must be occurring in other hairy regions of the upper body that is in contact with fabric.
For instance, the observation of tint fluff similar to BBL in the intergluteal cleft 1 is also consistent with the physical picture presented in this study, given that the body hairs in regions superior to the intergluteal cleft is oriented toward the cleft. Our results help to disprove the conjecture that the build-up of static-charge could play a role in the BBL production.
It is possible that the lint fiber will accumulate static charge due to friction. Further, since all the lint fibers are expected to have the same kind of charge, this theory also cannot explain the eventual amalgamation of all the fibers in one location.
Similarly, given the microscopic dimensions of lint fiber, one could reason that intermolecular surface forces e. In order to obtain a feel for the magnitude of these forces, we compared the experimentally measured pressure due to adhesive forces between lubricated ultra-smooth silicon surfaces 16 with the skin pressure induced by garment; both are found to be of the same order.
However, since the surfaces of lint fiber, cloth and hair are not smooth and the area of surfaces in contact is very little, the magnitude of short-range forces is expected to be negligible in the present problem. Notwithstanding, the effect of such forces can be accommodated in the present model by suitably changing the pressure experienced by the lint fiber in Eq.
To conclude, we have presented a theoretical model to understand the phenomenon of formation of navel fluff. We hypothesize that the combined action of the oscillatory motion of the shirt induced by breathing and the microscopical saw-tooth serrations due to the overlapping cuticle scales on the abdominal hairs stooping towards the navel leads to a perpetual production of lint fibers on the body, which is channeled to the navel, where the BBL builds up.
Our model quantifies this hypothesis and shows that the mass of BBL in the navel increases linearly with time initially Eq. Removing your belly hair could also limit your lint build-up. Contact us at letters time. By Markham Heid. Poor Georg Steinhauser. Related Stories.
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