The National Safety Council defines occupation illness as any abnormal condition or disorder, other than one resulting from an occupational injury, caused by exposure to environmental factors associated with employment. It includes acute and chronic illnesses or diseases that may be caused by inhalation, absorption, ingestion, or direct contact. Occupational illnesses are often times hard to recognize. Therefore, the number of reported cases is thought not to reflect the actual number of instances of occupational illnesses. Because there are many cases of occupational illnesses that are not categorized as such, preventing them becomes a problem. Documentation is critical to proving occupational illness, and even then, the findings are usually disputed, and in many cases, successfully.