Lora from HealthUnlocked has just let me into a little secret. This site supports a very small subset of bbcode formatting, which enables you to format text by setting it to bold, italicised or underlined.
Basically, you just surround the text you want to format with [n] and [/n] pairs (where n is b, i or u as required) thusly:
[ b ] word(s) you want in bold text [ /b ]
[ i ] word(s) you want in italicised text [ /i ]
[ u ] word(s) you want underlined [ /u ]
(I've left spaces between the square brackets and the formatting character so you can see how it is done.)
You can even get really carried away and have underlined and italicised bold text!