Why does your back itch after you cough a?

Answer 1

I have this sensation too. It is not skin related (unless it is an allergic reaction that makes you both cough and have a rash), but rather a nervous symptom - that is, related to the nerves in your chest. A cough is produced when the diaphragm (the large breathing muscle that your lungs sit on top of) rapidly expands, and at the same time, the throat is closed shut. This quickly builds up a pressure within the lungs. Then, when the throat is suddenly opened, the air is forced out with a coughing sound, and hopefully whatever it is that causes the cough (like irritating phlegm), will be expelled. The constant and repeated moving around of the diaphragm and lungs inside your chest will sooner or later start to irritate the nerve fibres in that area - the become overstimulated. Since many of our "internal" nerves (as opposed to nerves in the skin) are of a kind that we can´t readily feel, the brain becomes a bit confused.

It will place the sensations of these nerves not inside your chest, but on the surface of your skin - in this case, as an itch between your shoulder blades. This is called "referred sensation", and is the same phenomenen that makes an inflammated appendix cause an ache around the belly button.

As you may or may not have noticed, this coughing-back-itch will not easily be scratched away like a regular itch. This is because it comes from the inside of the body, and not from the outside like if you were being tickled by a feather or had lice.