What is Disease? "A disease is a condition that deteriorates the normal functioning of the cells, tissues, and organs." Diseases are often thought of as medical conditions that are characterized by their signs and symptoms. The disease can also be defined as: "Any dangerous divergence from a functional or normal state of an entity." When a person is inflicted with a disease, he exhibits a few symptoms and signs that range from normal to severe depending upon the medical condition. Hence, in order to identify different diseases, the normalcy of an entity needs to be studied and understood as a clear demarcation between disease and disease-free is not always apparent. The diseases are usually caused by many factors rather than a single cause. When we have a disease, we eventually show some signs, such as headaches, cough, cold, weakness. These signs are referred to as "symptoms." In almost all diseases, symptoms are shown immediately after having been struck by the disease. However, it varies depending upon the seriousness of the disease. Types of Diseases Diseases can be of two types Infectious diseases Non-infectious diseases Infectious Diseases Diseases that spread from one person to another are called communicable diseases. They are usually caused by microorganisms called pathogens (fungi, rickettsia, bacteria, viruses, protozoans, worms). When an infected person discharges bodily fluids, pathogens may exit the host and infected a new person (sneezing, coughing etc). Examples include Cholera, chickenpox, malaria etc. Non-infectious Diseases These diseases are caused by pathogens, but other factors such as age, nutritional deficiency, gender of an individual, and lifestyle also influence the disease. Examples include hypertension, diabetes, and cancer. They do not spread to others and they restrain within a person who has contracted them. Alzheimers, asthma, cataract and heart diseases are other non-infectious diseases.
Based on these above classifications, a disease may fall into any number of these classifications. Degenerative Diseases They are mainly caused by the malfunctioning of vital organs in the body due to the deterioration of cells over time. Diseases such as osteoporosis show characteristics of degenerative diseases in the form of increased bone weakness. This increases the risk of bone fractures. When degeneration happens to the cells of the central nervous system, such as neurons, the condition is termed as a neurodegenerative disorder. Alzheimer's is a prominent example of this disorder. Degenerative diseases are usually caused by ageing and bodywear. Others are caused by lifestyle choices and some are hereditary. Allergies An allergic reaction arises when the body becomes hypersensitive to certain foreign substances called allergens. This usually happens when the immune system reacts abnormally to any seemingly harmless substances. Common allergens include dust, pollen, animal dander, mites, feathers, latex and also certain food products like nuts and gluten. Peanuts and other nuts have the capability to cause severe allergic reactions that may induce life-threatening conditions such as difficulty in breathing, tissues swelling up and blocking the airways and anaphylaxis shock. Other common and less life-threatening symptoms include coughing, sneezing, running nose, itchy and