This is the most common type of back pain. The majority of cases of sudden-onset (acute) low back pain are classed as nonspecific. This is the type of back pain that most people will have at some point in their life. It is called nonspecific because it is usually not clear what is actually causing the pain. In other words, there is no specific problem or disease that can be identified as the cause of the pain. The severity of the pain can vary from mild to severe. This type of back pain is discussed further below.