The hairs found just inside the nostrils, known scientifically as vibrissae, serve a distinct purpose in the human respiratory system. As people age, these hairs often become thicker, coarser, and appear to grow much faster. This change is not due to an increased growth speed, but rather an alteration in the fundamental biological process that governs hair growth. Understanding this phenomenon requires examining the protective role of nasal hair and the complex cycle of the hair follicle.
The Protective Role of Nose Hair
The primary function of the vibrissae is to act as a preliminary air filtration system for the body. These stiff, short hairs form a physical barrier at the entrance of the nasal passages, catching airborne particulates from inhaled air. The vibrissae work in conjunction with the thin layer of mucus that coats the nasal lining, which helps capture and hold onto the particles. Research suggests that a higher density of nasal hair may be associated with a decreased risk of developing asthma in individuals who experience seasonal allergies.
Understanding the Hair Growth Cycle
All hair on the human body, including the vibrissae, grows and renews itself according to a predictable, cyclical pattern involving three main phases. The first and longest phase is Anagen, the period of active growth where the hair follicle produces the hair shaft. The duration of this phase is the primary determinant of how long a hair can grow before it is shed. Following active growth is the Catagen phase, a brief transitional period where the hair follicle shrinks and growth slows considerably.
The cycle concludes with the Telogen phase, the resting period during which the hair is no longer growing and remains anchored until it is shed. Each hair follicle operates independently, ensuring that not all hairs are in the same phase simultaneously. The length of the Anagen phase varies dramatically across the body. For example, scalp hair can remain in Anagen for two to seven years, while nose hair normally has a much shorter Anagen period.
Why Growth Speeds Up With Age
The perception that nose hair grows faster with age is linked to a change in the duration of the Anagen phase, not the speed of growth itself. As a person ages, hair follicles in the nose, ears, and eyebrows develop an increased sensitivity to circulating androgen hormones. Androgens, such as testosterone and dihydrotestosterone (DHT), are present in both men and women. This heightened sensitivity causes the nasal hair follicles to spend a significantly longer time in the active Anagen phase.
A prolonged Anagen phase means the hair shaft is produced for a greater period, resulting in hairs that are noticeably longer, thicker, and coarser. This change gives the impression that the hair is growing at an accelerated rate. Interestingly, the same androgen hormones that lengthen the Anagen phase in the nose often cause the Anagen phase on the scalp to shorten. This shortening leads to the gradual thinning and hair loss associated with male-pattern baldness, while the nose and ear hair reacts oppositely, leading to increased prominence of vibrissae in later life.