Asthma is a condition affecting the lungs and the breathing airways, and it is becoming increasingly common throughout the world. In Western countries especially, incidences are far in advance of where they were half a century ago, leading to speculation that modern building materials or factors in the environment could be causing the problem, especially for adult onset asthma. The condition is becoming more common throughout the world, however, and there is still no consensus of opinion as to what the exact causes are.