Why are fine hair and mucus present in our nostrils? Why should we not breathe in by mouth?

Fine hair, known as cilia, and mucus are present in our nostrils to help filter, warm, and humidify the air we breathe in. Here's why they are important:

1. Filtering: The fine hairs, or cilia, in our nostrils act as a physical barrier to trap large particles, such as dust, pollen, and bacteria, from entering our respiratory system. These trapped particles are then moved by the cilia toward the throat, where they can be swallowed or expelled through coughing or sneezing, reducing the risk of respiratory infections and irritation.

2. Warming: The nasal passages are lined with blood vessels that help to warm the air we breathe in before it reaches the lungs. This is important because cold air can irritate the respiratory tract and trigger symptoms such as coughing and wheezing.

3. Humidifying: The mucus produced by the mucous membranes in our nasal passages helps to moisten and humidify the air we breathe in. This is essential for maintaining optimal moisture levels in the respiratory tract, as dry air can lead to irritation, inflammation, and discomfort.

Breathing through the mouth bypasses the filtration, warming, and humidifying functions of the nasal passages, which can have several negative consequences:

1. Reduced Filtration: Breathing through the mouth bypasses the cilia and mucus in the nasal passages, increasing the likelihood of inhaling harmful particles, allergens, and pathogens directly into the lungs. This can increase the risk of respiratory infections and exacerbate existing respiratory conditions such as asthma and allergies.

2. Cold Air Irritation: Mouth breathing allows cold air to enter the respiratory tract without being warmed by the nasal passages, which can irritate the airways and trigger symptoms such as coughing, throat irritation, and bronchoconstriction.

3. Dryness: Mouth breathing can lead to dryness of the throat and mouth, as well as a dry cough. This can be uncomfortable and may contribute to problems such as bad breath, mouth  health issues, and difficulty swallowing.

Overall, breathing through the nose allows for optimal air filtration, warming, and humidification, helping to protect the respiratory system and maintain overall respiratory health.