There are many websites out there with excellent advice on cycling in hot weather. Suggestions include cycling slowly, wearing breathable fabrics, drinking plenty of water, applying sunscreen, and using baby wipes - all of which I do. And there tends to be a consensus that once the heat and humidity get past a certain point (yesterday's 100F weather would probably qualify!), there is just nothing that can be done other than bringing a change of clothes to work, particularly if one works in an environment with a dress code.
While this is good advice for some, changing upon arrival is not an option in my line of work. I have meetings in different parts of the city in the course of the workday, and there is no reasonable opportunity to change upon arrival prior to joining the meetings. Plus, I am on a tight schedule and changing a half a dozen times a day would be ludicrous.
So, what to do? Well, the Boston Globe and Bike Snob have already quoted me on this, but I've never actually written it in a Lovely Bicycle post: I wear fabrics with prints, which helps to disguise the one part of commuting in the heat we cannot control - sweat! "Eww gross!" - I know. But a reality none the less!
The best sort of prints for this purpose are small and detailed with some tonal variation - such as florals. This tricks the eye into not noticing additional tonal variations that happen from sweat stains. Stripes, polka dots, and other busy prints can work as well - but micro-florals and paisleys are particularly effective, because the patterns they form are organic. It may seem too simple of a solution, but this really is an amazing technique at making a sweat-soaked blouse, skirt, or dress look no different from a dry one.
I wore this dress to a meeting after cycling in it for 30 minutes in intense heat and humidity. Can you tell it's wet and disgusting? My colleagues could not, and complimented me on staying so cool in the heat. Yeah, right! Well, at least I can fake it with florals.