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It happens to us all at one time or another. You go to bed with a little cut on your finger and wake up to a hot, red, and painful sore. What causes these symptoms? How do you know if your wound is infected? What does your body do to fight infection?

What is infection?

At its most basic definition, an infection is a disease that is caused by microorganisms. The most common infections are caused by bacteria that enter your body at a wound site. These bacteria begin to multiply, invading the surrounding tissues and releasing harmful toxins.


The symptoms that we see are not actually caused by the bacteria themselves. Rather, we see our body’s response to these bacteria. The damaged tissues send out a chemical signal that tells our body to begin the inflammatory process. This process is our body’s method of killing the invading bacteria, destroying damaged tissue, and getting us back to normal. 

There are five classic signs that your body is fighting off an infection at a wound site.  They are pain, redness, swelling, heat, and loss of function.


The first classic sign is pain, especially pain that increases when pressure is applied to the site. The process of fighting invading bacteria is not a gentle one. Your white blood cells release toxic chemicals and tissue-destroying enzymes in order to destroy foreign microorganisms and break down damaged tissues. As you might expect, the site of this battle can become very tender and sore. 

Applying cold compresses can help reduce the pain and make it more manageable.


Along with pain comes redness. The white blood cells are carried to the infection site by your circulatory system. This means that your body responds to the damaged area’s call for help by increasing blood flow to the site. The vast majority of cells in your blood are red blood cells, so the redness that accompanies infection is simply a visible sign of extra red blood cells at the infection site. 


The third sign of infection is swelling, also known as edema. The main cause of this swelling is damage to the capillary endothelium. Capillaries are the tiniest parts of your body’s circulatory system. They are the places where your blood cells actually interact with your body tissue. 

The inflammatory process causes damage to this area and can interfere with your body’s ability to disperse fluids efficiently.

Extra fluid can become trapped at the infection site and this causes the area to swell.

As with pain, cold compresses can help to reduce swelling. It is also helpful to elevate the area, if possible, in order to promote drainage. This is especially useful when the infected site is on an extremity, such as your hand or foot.

Continue reading after recommendations

  • Infection. (2001). In Taber's Cyclopedic Medical Dictionary (pp.1043-1046, Edition 19). Philadelphia, PA: F. A. Davis Company.
  • Mindmap by
  • Photo courtesy of Bashar Al-Ba'noon by Flickr :