This doesn't work:
*emphasized_text*
_emphasized_text_
*emphasized*text*
_emphasized*text_
This works:
<i>emphasized_text</i>
**more_bold**
**more*bold**
If you want to italicize a word containing an underscore:
like_this
_like\_this_
If you want to italicize a word containing an asterisk
like*this
_like\*this_
We do not support intra-word Markdown emphasis. If you need that use HTML tags.
This is by design. For context, see:
http://blog.stackoverflow.com/2008/06/three-markdown-gotcha/