I am familiar with desensitization. For example, if you are afraid of driving, driving every day will eventually reduce your fear, desensitizing you.

But today I came across another concept, that of sensitization. I looked up the wiki article on [Sensitization](https://en.wikipedia.org/wiki/Sensitization), which says at the end,

> 
> Sensitization may also contribute to psychological disorders such as post-traumatic stress disorder, panic anxiety and mood disorders.
> 
> 
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So which is it then? What determines whether repeated exposure to something sensitizes someone or desensitizes them? With the example of PTSD, for instance, should not repeated exposure to war actually desensitize people?

I searched google scholar but could not find a paper that discusses both sensitization and desensitization. Mostly discuss the latter, in terms of reducing fears. 

Appreciate any references or books that might help me understand this. 

Thanks you.