If you can pass off as Egyptian, I'd suggest you dress a little more conservatively if you want to avoid the worst of the petty catcalls (harmless but a nuisance nonetheless). Otherwise, they'll think you're a disrespectful local lass.

You really need protection for your head as the sun is brutal in summer. I'd only suggest wearing a higab, if anything, for practical reasons, and then, only if you're Muslim. Otherwise, a broad-rimmed hat will do. It will mark you out as a tourist, however, but you don't want to get heat stroke like I did once - not a nice experience!

I met a Swiss girl in Cairo who had quite a dark complexion and could easily pass off as a local. She received none too subtle comments about her dress until she made it clear that she was a foreign tourist which immediately shut the sleazebags up.

BTW, I'm a guy, so everything I've said is from observation and hearsay not from personal experience!