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The body is constantly defending against attacks from pathogens. The first lines of defence against infection stop the pathogens from entering your body. These first lines are general defences, and are not specific to fight against certain types of pathogen. We call these non-specific barriers, and they can be either physical or chemical.

Skin

The skin covers almost all parts of your body to prevent infection from pathogens. If it is cut or grazed, it immediately begins to heal itself, often by forming a scab. This prevents infection as the skin acts as a physical barrier. Parts of the body that do not have skin have developed other ways to prevent infection. For example, the eyes produce tears which contain enzymes, and these are known as chemical barriers.

Nose

The nose has internal hairs, which act as a physical barrier to infection. Cells in the nose produce mucus which traps pathogens before they can enter the lungs. When the nose is blown, the mucus, and any pathogens that are trapped within it, is removed.

Trachea and bronchi

The trachea runs from the larynx (voice box) to the bronchi. The cells that line the trachea have hairs called cilia, which are much smaller than those in the nose. These are called ciliated cells. The ciliated cells waft their hairs and move mucus and pathogens upwards towards the throat where they are swallowed into your stomach.

Other cells called goblet cells create the mucus in order to trap pathogens. The production of mucus in your airways is a physical barrier.

Stomach

Stomach acid does not break down food in the same way as enzymes. It is part of the body’s non-specific first line of defence. It contains hydrochloric acid, and while it does us no harm, it is strong enough to kill any pathogens that have been caught in mucus in the airways or consumed in food or water. Stomach acid is a chemical barrier against infection.