During an inflammatory response to injury, why do swelling, redness and warmth occur?

1 Answer
Jul 13, 2016

It has to do with widening of the vessels to get enough immune cells at the site of inflammation.


The four classical signs of inflammation are:

  • rubor = redness
  • calor = warmth
  • dolor = pain
  • tumor = swelling

When an immune response is initiated, for example in the skin due to a cut, the immune system is alerted. The immune system then directs an army of immune cells to the site of inflammation to clean it up.

To get the immune cells as quick as possible in the right location, the small vessels around the lesion have to dilate. This dilation causes more blood flow in that area, causing the redness. Blood is also warmer than the skin, which explains the warmth.

In addition, the blood vessels that are dilated also have to be more permeable to allow immune cells to get into the tissue. This increased permeability also leads to fluid leaving the vessels into the skin. This causes swelling and also pressure that causes pain.

So, inflammation is a sign that your immune system is working really hard to clean it up for you!