Why do people touch their nose while speaking?

People Touch their noses when a negative thought comes to their minds through any of their senses. If a person hears something he didn't like, he might touch his nose (See also why people touch their faces while speaking).

If a person is reminded of something he dislikes, for example he is asked about the low grades he got, he might feel like touching his nose.

If a person see something unpleasant such as a scratch on his new car then he might feel like touching his nose.

When a person thinks of a negative thing his blood capillaries might contract and as a result he might feel like touching his nose.

If a person lies and at the same time believed that lying is a bad thing, he might feel like touching his nose. People who don't think that lying is bad are very likely not to touch their noses while lying.

If a person experienced feelings that he didn't like then he might feel like touching his nose. Again the fact that those feelings were believed to be a negative thing resulted in the desire to touch the nose (See why some people fold their arms).

The act of touching the nose is done by humans all around the world and has weak connection to any specific culture.

Any negative conclusion that mind makes can force a person to touch his nose. The itching is usually very hard to resist and in most cases a person will hardly be able to prevent himself from doing it.

A cold or any factor unrelated to psychological reasons can lead to nose touching however in most cases a psychological reason is present.