The most common respiratory condition in adults is probably the common cold. If you have experienced a sore throat, runny nose, blocked sinuses and a cough, then you are one of many people who have had a cold. A cold is usually caused by a virus that affects the upper respiratory system, and you will usually start feeling better after a few days (and up to a week). If you have caught influenza (the flu), you may feel sicker for a bit longer and you are likely to have a high fever and feel achy. But a healthy adult should recover after a week or so from the flu.
However, other respiratory conditions that affect many adults are not as simple as the common cold or the flu. When a viral or bacterial infection causes infection of the alveoli -- the tiny air sacs through which oxygen transfer to the body takes place -- this may cause pneumonia. Chronic obstructive pulmonary disease (COPD) refers to a group of diseases that make breathing difficult. COPD is one of the most common respiratory diseases and is usually experienced as chronic bronchitis or as emphysema. In emphysema, the alveoli lose their shape and collapse, trapping air inside of them and making it difficult to breathe out. The most common cause of COPD is smoking. Smoking is also a common cause of lung cancer, which is another common respiratory disease in adults.
Many adults suffer from asthma, although it is less common in adults than it is in children, since people often outgrow asthma after childhood. Adult-onset asthma is more common in women than men and is often triggered by sensitivity to allergens.