Allergies occur when your immune system reacts to a foreign substance — such as pollen, airborne particles or pet dander — or to a food that doesn’t cause a reaction in most people. Your immune system produces substances known as antibodies. When you have allergies, your immune system makes antibodies that identify a particular allergen as harmful, even though it isn’t. When you come into contact with the allergen, your immune system’s reaction can inflame your skin, sinuses, airways or digestive system.

Acute sinusitis causes the cavities around your nasal passages (sinuses) to become inflamed and swollen. This interferes with drainage and causes mucus to build up. With acute sinusitis, it might be difficult to breathe through your nose. The area around your eyes and face might feel swollen, and you might have throbbing facial pain or a headache.

Asthma is a condition in which your airways narrow and swell to produce extra mucus. This can make breathing more difficult and trigger coughing, wheezing, and shortness of breath. Asthma can’t be cured, but its symptoms can be controlled.

The common cold is a viral infection of your nose and throat (upper respiratory tract). It’s usually harmless, although it might not feel that way. Many types of viruses can cause a common cold. Influenza is a viral infection that attacks your respiratory system — your nose, throat, and lungs.

Snoring is the hoarse or harsh sound that occurs when your breathing is partially obstructed in some way while you’re sleeping. Snoring occurs when air flows past relaxed tissues in your throat, causing the tissues to vibrate as you breathe, which creates those irritating sounds.

Chronic obstructive pulmonary disease (COPD) is a chronic inflammatory lung disease that causes obstructed airflow from the lungs. Symptoms include breathing difficulty, cough, mucus (sputum) production, and wheezing. Emphysema and chronic bronchitis are the two most common conditions that contribute to COPD. Chronic bronchitis is inflammation of the lining of the bronchial tubes, which carry air to and from the air sacs (alveoli) of the lungs. It’s characterized by a daily cough and mucus production.

Cystic fibrosis is an inherited disorder that causes severe damage to the lungs, digestive system, and other organs in the body. Cystic fibrosis affects the cells that produce mucus, sweat, and digestive juices. These secreted fluids are normally thin and slippery. But, in people with cystic fibrosis, a defective gene causes the secretions to become sticky and thick. Instead of acting as a lubricant, the secretions plug up tubes, ducts, and passageways, especially in the lungs and pancreas.