It is the most basic instinct of any living thing to fight to survive. It is for this same reason why the history of mankind has been constantly marked by various armed battles. Disputes arise because of conflicts between ideologies and religion. The desire to acquire others' resources and dominate other territories have spawned wars. Since the beginning of time, man has not experienced a respite from bitter struggles that have brought terrible death and destruction.

In a smaller scale, another battle rages on. Bacteria, viruses and other molecular elements can be seen as parties in conflict inside the new battlefield --- the human body. People are already familiar with the methodology of warfare maybe because it has been frequently taught in history classes and shown in movies. However, maybe only a few are aware of how this same process occurs within the human body.

In this case, a person's body is considered the territory with all its abundant resources. The division that protects the territory, just like the armed forces in different countries, is called the immune system. If the armed forces makes use of a group of people and weaponry for defense, the immune system also has its group of cells and chemicals. As a systemic and carefully organized scheme is needed in fighting in order to win, the protecting system of the human body also makes use of what seems to be a well-planned strategy. Like any other system, however, human immunity also has its weaknesses and imperfections.

The immune system is created to protect the body from dangerous intruders called pathogens. A pathogen, upon invasion of the territory, will seek to utilize its resources in order to survive. The survival of the pathogen within the body results to infections. The type of infection that develops corresponds to the kind of pathogen that has formed it. It can either be a viral infection such as in common colds, a bacterial infection like cholera, a fungal infection such as candidiasis (yeast infection) or a parasitic infection like malaria. Either way, infections cause diseases that are detrimental people and may further lead to their death. However, the human body, just like any other territory, will not just stand by during the invasion. Upon detection of intruders, its immune system will automatically react with the similar instinct to survive.

Coded instructions within cells and other substances enable a strategically implemented process of protection. When pathogens enter the initial barrier of the body, they instantly harm the cells that they come upon. As the cells are injured or infected, it instantly releases eicosanoids and cytokins. These two serve as signals that will cause further reaction within the immune system. Eicosanoids cause the blood vessels to dilate so that the blood will rush in to the area and it also attracts white blood cells to respond. The increased blood flow results to inflammation which is characterized by redness and and swelling. Cytokins on the other hand help in the communication between white blood cells that will eliminate the pathogen, attract more immune cells like killer T-cells and promote healing of the area damaged by pathogens. This mechanism of the immune system, however, as said earlier has its weaknesses and imperfections.

Some pathogens, being more complicated to destroy, sometimes have better chances of survival and to proliferate. When a human's immune system is not anymore able to fight, external help is already needed such as antibiotics. Several antibiotics, however, are not 100% efficient and leave some bacteria to survive. These remaining bacteria often develop antibiotic resistance, particularly to those that have already been used against them and can cause a more dangerous health problem. Newer antibiotics are then necessary in these situations.