I've said this before, and I'll say it again. I sweat a lot. Add in New York City's heat and humidity — and those Subway platforms that feel like the air is 800 degrees — and I've really needed to rethink how I get dressed for summer and hot fall days. Sure, it took some time to learn about the don'ts — jeans, long-sleeves, and silk — and do's, like breezy linen pants, sandals, crop tops, and one secret hero staple I'm about to reveal, but I think I've finally nailed it.

I was propelled to spill my no. 1 summer style secret after seeing Hilary Duff in it earlier this week. No, I'm not talking about skorts, though those are also brilliant, too; I'm referring to those exercise dresses I used to wear only on the tennis court but now wear all over New York. They've been my summer lifesavers, and I plan on wearing them well into fall as well.

Exercise dresses are wholly uncomplicated, one reason I love them so. But their easygoing appearance is not to be underrated because they do the darn thing better than most traditional dresses. That's because they're made from sweat-wicking material, like that of your go-to leggings and sports bras, which makes them ideal for hot summer days. Many are designed with hidden shorts (no chance of flashing with these), and often hidden pockets in said shorts for safe storage of your tiniest essentials. Now you get why it's my hero piece, right?

Shop now: $88; girlfriend.com

Shop now: $88; outdoorvoices.com

Shop now: $108; nordstrom.com

Shop now: $98; thereformation.com

Don't be deterred by the workout aspect, either — so many of the options out there go above and beyond their high-performance fit and material. They're fashionable thanks to brands like Outdoor Voices and Girlfriend Collective that are churning out styles with fresh, fashion-forward details like cutouts and halter necklines. LBD? Meet the LBED (aka little black exercise dress). It's just as chic, but way more practical.

I wear mine for everything from running Sunday errands to dinner dates with friends, swapping accessories accordingly. My daytime sneakers are replaced with chunky black boots and I trade in my baseball cap for gold hoop earrings and sparkly jewels. With said additions, you'd never know I was wearing an exercise dress. It's my little secret, and that's why I love wearing it.

So, take my word for it (Duff's, too): End-of-summer summer and fall dressing is going to be a lot less daunting with an exercise dress on hand. Shop some of the best below.

Shop now: $88; nordstrom.com

Shop now: $79; nordstrom.com

Shop now: $98; thereformation.com

Shop now: $108; aloyoga.com

Shop now: $110; kittyandvibe.com