Pus is a thick, yellowish or greenish fluid that accumulates at sites of infection. It is indeed a byproduct of the body's defense mechanisms, specifically the immune system's response to invading pathogens like bacteria. While pus formation is a sign that your body is fighting off an infection, it is considered harmful—or "poisonous" in a manner of speaking—because of its composition and potential effects on surrounding tissues.

Here's why pus is both a defense mechanism and potentially harmful:

Composition of Pus:
White Blood Cells (Neutrophils): When an infection occurs, white blood cells called neutrophils rush to the site to attack the invading bacteria or pathogens.
Dead Cells: The battle between neutrophils and pathogens results in the death of both immune cells and bacteria, as well as some surrounding tissue cells.
Pathogens: Live bacteria or other microorganisms can be present within the pus.
Toxins: Bacteria release toxins as they multiply, and dying cells release enzymes and substances that can damage tissue.
Environment for Bacteria:
Breeding Ground: The warm, nutrient-rich environment of accumulated pus can serve as an ideal breeding ground for bacteria, allowing them to multiply further.
Anaerobic Conditions: In some cases, the area may become oxygen-deprived, favoring the growth of anaerobic bacteria, which can cause more severe infections.
Potential Spread of Infection:
Adjacent Tissues: Pus can erode surrounding tissues, allowing bacteria to invade deeper into the body.
Bloodstream: If bacteria from the pus enter the bloodstream, they can spread to other parts of the body, leading to systemic infections like sepsis, which is life-threatening.
Formation of Abscesses: An abscess is a pocket of pus that can cause pressure and damage to nearby organs or structures.
Inflammatory Response:
Enzymes and Chemicals: The substances released by dying cells and bacteria can trigger excessive inflammation, which, while part of the immune response, can cause additional tissue damage and pain.
Tissue Necrosis: Prolonged inflammation and the presence of pus can lead to tissue death (necrosis), complicating the healing process.
Delayed Healing:
Interference with Repair Mechanisms: Pus can interfere with the normal healing process by preventing the closure of wounds and encouraging continuous infection.
Scarring: Chronic pus formation and infection can lead to significant scarring and loss of function in the affected area.
In Summary:

While pus indicates that your immune system is actively fighting an infection, its presence is a double-edged sword. The accumulation of dead cells, live pathogens, and toxic substances creates a harmful environment that can damage tissues and facilitate the spread of infection. This is why medical intervention often involves draining pus from abscesses and treating the underlying infection with antibiotics to prevent further complications.

Preventive Measures and Treatment:

Proper Wound Care: Keeping wounds clean and covered to prevent infection.
Medical Attention: Seeking prompt treatment for signs of infection (redness, swelling, warmth, pain, pus formation).
Antibiotics: Using prescribed medications to eliminate bacterial infections.
Drainage Procedures: In some cases, surgical intervention is needed to remove accumulated pus.
Remember, while pus signifies an active immune response, it also necessitates appropriate medical care to ensure that the infection is resolved safely and effectively.를 한국어로 번역