Located strategically at the entrance of our respiratory system, the humble nose hair serves multiple purposes beyond the aesthetic. Often overlooked, these hairs constitute our first line of defense against environmental pathogens such as germs, fungi, and spores. Their protective role doesn’t stop there; when insects or irritants touch our nostril hairs, it triggers a reflexive sneeze, the body’s effective method of expelling intruders. The nasal hairs’ ability to provide such alarms underscores their significance in maintaining our health.
Nose hair and filtration: Primarily, nose hairs function as a filtration system. Particles enter the nose via the nares (nostrils), with larger particles (> 3 µm) accumulating in the nose’s anterior part. Thicker nasal hairs trap more coarse dust particles (> 5 µm) effectively than thinner nasal hairs. Moreover, as the nasal hair diameter increases, particle deposition on the nasal cavity wall decreases. Increasing nasal hair diameter decreases filtration efficiency for 5–7 µm particles but increases it for 7–15 µm particles.
In essence, hairs in the nose airway act as ram filters, trapping particles that are impacted into the hairs. However, one disadvantage to such systems, as with HVAC systems in buildings, is that they must be cleaned periodically to remove particles and permit air to flow. In the nose, this normally occurs through the act of sneezing, though mucus can also help as part of the cleaning process.
Increased nose hair length provides a larger surface area for dust particles to be deposited, leading to increased filtering efficiency. However, there are considerable individual differences in the quantity, diameter and length of nasal hair and consequently this causes variations in nose filtering efficiency. Reduced clearance of allergens due to decreased filtering efficiency can heighten the risk of asthma development in allergic rhinitis patients. So if you have lots of thick, long nose hair, be proud of your effective particle filtration system!
Nose hair, temperature control and humidity: Beyond filtration, nasal hairs also contribute to regulating the humidity and temperature of inhaled air. In fact, physiologically, it’s easier to extract oxygen from warm humid air than from cold dry air. Nose hairs increase the surface area over which mucus, the natural humidifier, spreads, helping to humidify the air passing through the nasal passages. Additionally, nasal hairs help to retain moisture from exhaled air, preventing the nasal passages from becoming too dry. This regulation of moisture levels is especially critical for the health of the entire respiratory system; warm humid air reduces the chance of tissue damage in the larynx and lungs.
The potential thermoregulatory function of nasal hair is worth exploring. Although published data on this is limited, nasal hairs may help warm the air in the nostrils in the same way as terminal hair elsewhere on the body. It has been suggested that people with fewer nasal hairs may have less ability to heat cold air, potentially increasing their risk of developing asthma and other nasal conditions such as post nasal drip. It’s even thought that, as early humans migrated into climates with drier air, they developed larger noses to help improve the air warmth and humidity as it is drawn in. No one has looked to see if there are more nose hair follicles in larger noses compared to smaller and/or flatter noses, but it seems reasonable to speculate that this is possible.
Nose hair structure: Nostril hairs are generally larger than scalp or axillary (arm pit) hair and often possess longitudinal grooves in the fiber which likely enhance the relative stiffness of the hair. Most hair follicles on the body are associated with arrector pili muscles. Notably, the arrector pili muscle does not develop in hair follicles growing perpendicular to the skin, such as eyelash hair follicles, follicles of the external ear canal, and those of the nasal orifice. According to a rather old study by Alverdes, the average width of the hair follicle of the nasal hair in humans is 0.16 mm. Similar sizes and shapes of nostril hair and nasal hair follicles are also seen in other animals. Although nose hairs are sometimes called “vibrissae”, the Latin word used to describe whiskers as seen in cats and mice etc., it’s not clear that they are the same kind of hair follicle.
Number of nose hairs: According to a recent study by Pham et al., the average nasal hair counts in the left and right nostrils are approximately 120 and 122.2 respectively, while the distance from the nostril opening to the deepest location where nasal hair grows ranges from 0.81 cm to 1.035 cm. However, these numbers were produced by looking at people in their 80s. Another investigation found that patients aged less than 45 years had an average of around 41.75 nose hairs per 19.6 mm2. Women and men in this age group had 47.50 and 36.00 nose hairs per 19.6 mm2, respectively. On average, patients aged 45 years and older were found to have 28.63 hairs per 19.6 mm2. Women and men in this age group had 29.75 and 27.50 nasal hairs per 19.6 mm2, respectively. The data suggests that younger people have a higher density of nose hair than older people. Perhaps this apparent loss of nose hair as we get older is partially compensated for by growing longer nasal hair in an attempt to maintain filtration efficacy?
Nose hair loss: Studies have shown that nasal hairs play an essential role in particulate filtration, but very little is known about their distribution or changes that occur with age or follicular disorders. Interestingly, individuals with alopecia areata, particularly alopecia universalis who lack these filtrative hairs, report persistent runny noses and the lack of nose hair may potentially exacerbate asthma and allergic rhinitis in these people.
Nose hair pluck strength: As the nasal hairs trap foreign contaminants, they can accumulate and solidify within the nasal cavity. This build-up necessitates removal and with humans (and other primates) that often leads to nose picking; a process that may lead to painful nasal hair pull out along with the snot if the root is detached from the nasal dermis. Still more people pluck their nose hair to achieve a cosmetically acceptable look. But how much force is needed to pull out hair from the nasal orifice?
A study involving 100 nasal hair pullout measurements revealed several intriguing findings. Nasal hair pullout strengths were found to vary significantly, although the variability was relatively consistent within each subject’s nostril, with mean pullout strength values of 0.430 N and 0.293 N (Newtons) for Subject 1 and Subject 2 (the authors of the study), respectively. Interestingly, nasal hair thickness (diameter) did not correlate with required pullout force, with finer hairs occasionally demonstrating greater pullout strengths. A relationship was found between the root width-to-hair-diameter ratio and the required pullout force, with larger ratios generally corresponding to larger pullout forces. The study also noted a physiological response to nasal hair pullout, including sneezing and eye-watering, though this ceased after several consecutive hair detachments. Perhaps it should also be mentioned that this study was not funded and driven purely by the scientists own curiosity!
Conclusion: In sum, nose hair is a key player in our health and well-being, with functions extending from filtration to humidity regulation and potential thermoregulation. Despite often being regarded as a nuisance, nasal hair is an unsung hero of our body’s defense system. So, the next time you contemplate the aesthetic appeal of your nasal hair, remember, it’s not just hair, it’s a protective fortress.
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