Facial features exhibit remarkable diversity across the human population, and the size and shape of the nose are among the most noticeable traits that vary between individuals. Understanding why nostrils appear the way they do requires examining the underlying physical structure, the blueprint inherited from one’s parents, and the long-term influence of environmental forces on human populations.
The Anatomy of Nasal Apertures
The appearance of “big nostrils,” technically known as the nares, is determined by a complex arrangement of cartilage, bone, and soft tissue. The width of the nasal base, often referred to as the alar width, is the distance between the outer edges of the nostrils and is a key measurement. This width is largely defined by the shape and positioning of the lower lateral cartilages, which form the supportive framework of the nasal tip and the sidewalls of the nostrils.
These cartilages dictate the flare and contour of the nostril rims. The fibrofatty tissue that completes the contour of the nasal tip also contributes to the overall dimensions and projection. Therefore, the perceived size is not simply a matter of a single measurement but a proportional relationship between these underlying structural components.
The Role of Genetics and Inheritance
The specific size and shape of the nostrils are highly heritable, meaning they are primarily dictated by the genes passed down from parents. Facial features are considered polygenic traits, meaning their expression is influenced by the interaction of many different genes. A shared nasal structure among family members is a direct reflection of this genetic blueprint.
Several specific genes have been identified that play a role in sculpting the nose’s dimensions. For instance, the genes GLI3 and PAX1 have been linked to controlling nostril breadth, while the RUNX2 gene influences the width of the nose bridge. These genes are involved in the development and growth of bone and cartilage in the craniofacial region, establishing the individual framework that determines the ultimate size of the nasal apertures.
Evolutionary Adaptation and Climate
Beyond individual inheritance, the variation in nostril size across global populations is a result of long-term evolutionary adaptation to different climates. The primary function of the nose is to condition inhaled air, ensuring it is warm and moist before reaching the lungs. Nasal structure evolved to optimize this function based on the local environment of a population’s ancestors.
In populations whose ancestors lived in warm, humid climates, wider nostrils and a broader nasal base were favored. This configuration allows for the rapid exchange of air without the necessity for extensive warming or humidification. Conversely, narrower nasal passages are an adaptation for survival in colder, drier climates.
A narrower nostril slows down the airflow and increases contact time with the mucus-covered membrane inside the nose. This maximizes the surface area for warming and moisturizing the air, preventing damage to the lungs from cold, dry air. Studies have shown a correlation between nostril width and both temperature and absolute humidity, supporting the idea that natural selection has driven these population-level differences.
Non-Permanent Factors Affecting Appearance
While genetics and evolution set the underlying structure, several other factors can temporarily or permanently alter the appearance of nostril size. Temporary inflammation or swelling, such as that caused by severe allergies, a sinus infection, or a mild injury, can make the nostrils appear wider or more flared. The swelling of internal nasal tissues, or chronic rhinitis, physically occupies space and can push the external structures outward.
Age also contributes to a change in appearance due to the gradual weakening of supportive tissues. The loss of collagen and elastin causes the skin to thin, and the nasal cartilage can weaken and lose support, sometimes causing the nasal tip to droop. This change in projection can create the illusion that the nostrils are larger or more prominent over time. Furthermore, chronic inflammation or the presence of nasal polyps can exert pressure on the surrounding bone and cartilage, potentially leading to a gradual, permanent widening of the nose.