 Have you ever wondered why you get sick? How can some sicknesses happen on their own and why others caught from those around you? In this video, we're going to be talking all about diseases. We'll start with the definition of what disease is before discussing two major types of disease, infectious and non-infectious disease. So to start, what is a disease? A disease can be defined as a condition that impairs the structure or function of all or part of a living organism that is not a direct result of a physical injury. So this could include something like bronchitis, which affects your ability to breathe due to inflammation of the airways or diabetes, which affects insulin production in the body. Note that this definition includes any living organism. That's because other animals and even plants can get diseases. This basic definition is very broad. So let's break down the two major types of disease. Infectious diseases and non-infectious diseases. Infectious diseases are those that are contagious. This means that they can be transmitted from one sick organism to a healthy one, passing on the disease. Some examples of infectious diseases are the common cold and the flu, sexually transmitted infections such as HIV or chlamydia and gastroenteritis, also known as gastro or a stomach bug. While these diseases may all seem very different, they are all caused by pathogens. Put simply, a pathogen is any organism that can infect a host causing disease. These pathogens can grow on or inside an organism, affecting bodily functions and causing sickness. This is why these conditions are all called infectious diseases. The second main type of disease is a non-infectious disease. These diseases are not contagious, meaning that they can't be spread between organisms. Instead of being caused by pathogens, these diseases are generally caused by either genetics or lifestyle factors. Lifestyle factors that can cause disease can include diet and nutrition, as well as exposure to negative environmental factors. For example, UV radiation can cause melanoma and skin cancer and a poor diet can contribute to developing type 2 diabetes. Other examples of non-infectious diseases can include heart disease, type 1 diabetes and asthma. So in summary, a disease can be defined as a condition that impairs the structure or function of all or part of a living organism that is not a direct result of a physical injury. And there are two main types of disease, those that are infectious and those that are non-infectious. Infectious diseases are those that are contagious and can be transmitted from one organism to another. These diseases are caused by pathogens. Non-infectious diseases are not contagious and can not be transmitted. These diseases are caused by genetic and lifestyle factors or a combination of both.