Updated: Aug 9, 2020
Disease, any harmful deviation from the normal structural or functional state of an organism (Animal, plants, humans or insects etc), generally associated with certain signs and symptoms.
A disease can be caused by many things. Sometimes germs enter our body through food, water or air. A person can be infected by infectious agents like bacteria, viruses or fungus. Disease can also be caused by eating bad or old foods.
Pathogens are those agents that may cause a disease in a person. For instance; there may be a bacterial or a viral attack on some part of the body that causes feelings of pain and discomfort in the person. It may also include such pain or discomfort that is caused by a particular malfunctioning of the body due to other factors.
In medical terms, a disease is described as an abnormal condition in any organism that obstructs its bodily function. It may, in rare cases, even because the death of the person concerned. If we use it in a broader sense, it may even refer to disabilities and injuries, infections and deviant behavior. It is important to note that even the brain is a human organ, and is therefore prone to illnesses and disease. The main effect of a disease is felt when a particular organ of the body or the body as a whole fails to maintain its condition of balance and stability. This condition is referred to in medical terms as homeostasis.
It is important to note that both illness and disease result in more or less the same symptoms. However, an illness can be cured in most cases. For instance, cold, flu or gastrointestinal diseases can be cured by treatment. However, there are a number of diseases that cannot be cured. In medical terms, both are undesirable, as they interfere with the state of homeostasis.
Illness and sickness are both generally used as a synonym for disease. However, the term illness is occasionally used to refer specifically to the patient's personal experience of his or her disease,
A very simple definition which I personally like, it was I find in a comment section on a website, Disease is something that an organ has, illness is something a man has. Disease is something that needs to be cured, such as infection, injury, toxicity, cell degenerations etc. Illness is something that needs to be managed such as feeling of pain, discomfort, distress, weakness, fatigue etc. These two things are not mutually exclusive, they often occur together. Diseases usually causes illness but it can be without feeling of illness. For example cardiac disease, it is a silent killer, in it you don't feel any illness but you might die due to this disease. Similarly we have illness without disease. Example often pain occurs to a person but there is no diagnosable structural damage.