In the context of forensics, asphyxia is generally caused by an obstruction to the airwaves of some sort. This isn't necessarily the root cause; for instance, some allergies can cause the throat to swell up enough so that no air can get through.

The classic signs of asphyxia are:

  • Congestion of the face, because the blood has been trapped in the face, possibly because of strangulation (i.e., the veins in the neck have been compressed)
  • Oedema of the face
  • A blue tinge to the skin; this is because the blood hasn't been oxygenated. (Because there is no oxygen to oxygenate it with.)
  • Petechial haemorrhages in the skin, particularly around the eyes and behind the ears. These look like little red spots, and are due to raised blood pressure.