Final answer:
Illnesses known as noninfectious diseases, which include cardiovascular diseases, cancer, and those associated with obesity, are the leading health problem worldwide, influenced by lifestyle and environmental factors.
Step-by-step explanation:
Illnesses defined as noninfectious diseases are the leading health problem in the world today. These include conditions such as cardiovascular diseases, cancer, diabetes, and those related to obesity. Contrary to infectious diseases which are caused by external pathogens like bacteria and viruses, noninfectious diseases are largely associated with lifestyle choices and environmental factors. In high-income nations, issues like cancer and obesity-linked diseases such as heart disease are prevalent, and environmental concerns such as pollution contribute to these problems. In low-income countries, the health challenges often involve infectious diseases due to the lack of clean water and sanitation, malnutrition, and insufficient access to healthcare. However, global trends indicate that noninfectious diseases are on the rise in these countries as well due to changing lifestyles and urbanization. It is important to note that while medical advancements have been successful in combating certain diseases like smallpox and polio, new and re-emerging challenges like the COVID-19 pandemic highlight the ongoing battle against global health issues.