Wound and skin infections

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What are wound and skin infections?

Infections of skin and wounds are the consequence of invasion of tissues by one or more species of microorganisms. This infection triggers a response by the body's immune system, causes inflammation and tissue damage, and slows the healing process. Many infections remain confined to a small area, such as seen with an infected superficial skin scratch or hair follicle, and these often resolve on their own. Other infections may persist and, if untreated, increase in severity and spread further and/or deeper into the body. Some infections spread to other organs or cause septicaemia.

Skin is the body's largest organ and is its first line of defence. Even when clean, the surface of the skin is not sterile but is populated with a mixture of microorganisms called normal flora. This normal flora forms a dynamic barrier that helps to keep other more harmful microorganisms (pathogens) at bay. At any one time, a certain percentage of the general population will be carriers of a pathogen that displaces some of their normal flora and “colonises” locations like the mucous membranes of the nose. Most of the time normal flora and colonising pathogens do not cause illness, however if there is a break in the skin or if the immune system becomes compromised, then any of the microorganisms normally present can cause a wound or skin infection.

Wounds are breaks in the integrity of the skin and tissues. They may be superficial cuts, scrapes or scratches but also include more invasive insults such as punctures, burns or be the result of a surgical or dental procedure. The microorganisms likely to infect the wound depend on several factors:

  • on the wound's location on the body and its extent and depth
  • the external environment in which the wound occurs, such as water or soil
  • the injurious agent such as a thorn in gardening injuries or the bitumen in road trauma
  • the microorganisms present on the person's skin

The skin has three layers: the outer epidermis, the dermis (where many hair follicles and sweat glands are located), and the fatty subcutaneous layer. Below these layers are membranes that protect connective tissues, muscle and bone. Wounds can penetrate any of these layers and skin infections can spread directly into them. Wound healing is a complex process that involves many related systems, chemicals, and cells working together to clean the wound, seal its edges, and to produce new tissues and blood vessels.

Skin and wound infections interfere with this healing process and often create additional tissue damage. These infections can affect anyone, but people with underlying conditions such as poor circulation or a suppressed immune system are at greater risk of slowed wound healing  and subsequently at higher risk of infection. The infection may become a chronic infection if it penetrates deep into body tissues such as bone, or when the infection occurs in tissue that has inadequate circulation.

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