Why are 'sec-' and 'tert-' prefixes printed in italics?

While reading about nomenclature of branched alkyl groups, I read that certain common names are also approved by IUPAC. Among those names, only few prefixes are italicised (namely *sec-* and *tert-*) and others like iso and neo are printed normally. These names are documented in the [IUPAC blue book](http://www.acdlabs.com/iupac/nomenclature/79/r79_36.htm#a_2__25). What can be the reason for italicising *sec-* and *tert-* and leaving out the others?




From the ACD Labs page about [IUPAC italicization](http://www.acdlabs.com/iupac/nomenclature/93/r93_74.htm),it is stated that 



> 
> Italicizing mainly serves to mark letters which are not involved in the primary stage of alphabetical ordering.
> 
> 
> 


According to the [American Chemical Society Style Guide](http://aerosol.chem.uci.edu/intranet/files/ACS_style_guide.pdf) (p. 235), the use of italics for



> 
> positional, stereochemical, configurational, and descriptive
>  structural prefixes when they appear with the chemical name or formula. 
> 
> 
> 


(There are several prefixes in the list).


These are separated from the chemical name with a hyphen and are not capitalised 


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