Development of a disease depends on the nature of the disease, it maybe caused by microorganisms, so its development will start with an infection or the transmission where the individual is exposed to the causative agent, next is the incubation where microorganism inside the host multiplies, then the prodromal period when there is the appearance of symptoms, followed by the period of illness, then the period of convalescence or the period of decline when the person is about to get well.
If the disease is physiological in nature it develops due to unhealthy lifestyle, disease may start due to vices that leads to changes in tissues or deposition of unwanted chemicals or deposits that leads to defects of organs and tissues in the body.
