The summer heat can be a nuisance wherever you live, but particularly here in the southern US where the sticky humidity just amplifies the already insufferable temperatures. While that constantly sweaty feeling isn't going to be avoidable, choosing the right clothing will at least make your time in this environment a little more comfortable.
Fabrics and Fit
Possibly the most important aspect to look at when choosing what you'll wear on any adventure is looking at what it's made of, and how it fits. There are a few fabrics that would work well for a hot and humid environment.
Cotton: While lightweight cotton is a soft and fairly breathable material, it won't wick moisture away and off of your body. Otherwise it is a great affordable material to grab for a day of hiking. One of the main drawbacks of cotton is that because it just soaks up moisture, when the temperature drops at night you will be left in a cold wet shirt. Be sure to bring some dry clothes to change into if this would cause a problem for you.
Nylon/Polyester: These synthetic materials are great for wicking moisture away from the body, however they will retain odor easily. Breathability will depend on how tight the weave is knit, look for shirts made with a looser knit will be more breathable than something with a super tight knit weave (This is why wearing a basic rain jacket with no ventilation in this climate will feel like being trapped in a sauna)
Linen: Linen isn't something you would normally expect to go hiking in, but I would say it is definitely worth looking into! Linen is a plant based fabric with large fibers and very open weaves, making it very breathable and lightweight. It also is naturally odor resistant and fairly durable. It has the same weakness as cotton with it's inability to wick moisture away, like the synthetic materials or wool.
Merino Wool: An incredibly soft natural fiber that is well known to be moisture wicking, odor resistant, and can even be quite breathable. The only downside to merino wool (other than the steeper price) is that it's a little less durable than something like cotton or polyester.
Whichever fabric you choose, I find having your clothing fit a little bit looser to be better than something too skin tight. Since your sweat won't be able to evaporate away, at least keeping your clothes from clinging and rubbing against your skin can help just a little bit more with comfort.
Sun Protection
Keeping those harmful UV rays away from your skin is critical if you want to keep from getting sunburns, and protect your skin health. Look for UPF ratings whenever you're shopping for your clothing, they will usually be something like SPF 15, 30, 50+, etc. Obviously the higher the number, the more protection from UV rays you will have.
Many people like hiking in long sleeve sun-shirts, whether that's a button up shirt or just a simple long sleeve shirt. In very humid weather, wearing long sleeves will end up trapping in more moisture on your body. It can be a trade off some people are willing to make, while others may feel more comfortable in as little clothing as possible. Often a UPF rated short sleeve shirt or tank top will do just fine paired with sunscreen to protect your skin, and wearing a good wide brimmed sunhat will help keep the sun off your head, face, and neck.
Pants vs Shorts
Pants will generally be more protective than shorts, while shorts will obviously be great at keeping your legs cooler. What you choose to wear will be mostly up to what the environment will look like.
Wearing long pants will give you some much needed UV protection in the hot summer sun. They also provide protection from things like mosquitos, ticks, gnats, leeches and other annoying and potentially dangerous creepy crawlies. Another benefit of pants is that they will keep irritating plant life away from your skin as well. Brambles, poison ivy, vines, and other plants that you may rather keep off of your legs are very common through most hiking trails, especially here in the south east. I personally use the Outdoor Research Ferrosi Pants (here's a women's version)when I want to have that extra protection on a hike.
Generally for materials in pants something lightweight, fairly breathable, flexible but still durable is what you will want to look for. Pants designed for hiking will tend to be made of breathable, lightweight fabrics that will remain comfortable even after miles and miles of hiking. Plain old sweatpants or athletic pants will work just fine as well, but I would say stay away from heavy cotton based pants if you can.
Shorts main benefit will be the cooling factor as it will allow more of your skin to breath. While you will be more susceptible to the elements, you will feel a lot more comfortable and generally have a little more mobility than when wearing full length pants. The type of shorts you choose generally doesn't matter but I would wear some hiking specific shorts, or basic athletic shorts over something like denim shorts for example. I use a pair of North Face shorts similar to these, or I'll just wear any of my favorite gym shorts.
If you're having trouble choosing between pants or shorts, then convertible pants are the way to go! Many outdoor brands sell hiking pants that have zippers just above the knees, to take off the bottom half of the pants. With these you will have the protective benefits of long pants, while being able to turn them into more breathable shorts whenever you need to.
Socks and Shoes
Considering we're on our feet for the duration of a hike, it's a good idea to make sure they are as comfortable as possible.
With socks you will want to look for something that is breathable, moisture wicking (very important to prevent blisters and improve overall comfort), and that has just as much fabric as you need. Materials like merino wool or even some synthetic are going to work very well. Stay away from cotton in your socks like it's the plague just don't even think about it. Most good hiking socks designed for summer will be thin while still having some added cushion in critical areas for added durability and comfort. When choosing the correct cut of sock to use, make sure it is visible slightly above the top of your boot or shoe, allowing for as much skin to be exposed as possible while not allowing the boot to rub against you legs. One of my favorite socks are these Darn Tough no-show socks, these are more than capable paired with a good low shoe. We also carry Smartwool, as you can see with these women's no show socks!
Speaking of boots, let's talk about some footwear. the traditional hiking boot is becoming less and less popular these days with people turning towards the lighter trail runners and other hiking shoes. If you really want that extra ankle support the boot provides, I would recommend avoiding leather as much as possible. In these super hot muggy environments those leather boots will just trap all the heat and moisture with no way for it to get out. This creates a fairly unpleasant experience after a few miles down the trail and we would rather avoid this at all costs. Look for a boot that is made of sturdy but breathable materials, with nice sturdy outsole and ankle supports. I would recommend checking out the Keen Targhee III boots, which come in both a mid and a low top version
If lightweight mobility sounds more enticing to you, then look to the trailrunner. Trailrunners are basically just running shoes with some beefier lugs and a little more durability to be more than capable on off road excursions. Don't let the name throw you off however as you'll find not only runners sporting these, but also through-hikers, and casual day hikers alike. A good trail shoe will be much more breathable and feel less stiff and clunky than boots or hiking shoes generally are. You can even find some that are waterproof if that's a concern for you. ON Running makes a great, super comfortable trail runner with the Cloudventure.
Conclusion
Overall just wear whatever you find to be the most comfortable. If you would prefer to tackle the trails dressed up in full on chainmail and a cloak like you're on a mission to Mordor, then knock yourself out. Personally, what works best for me is throwing on a synthetic t-shirt, gym shorts, some lightweight wool socks, and whatever trail shoe suits my fancy. This outfit will last me through the summer months and around here, most of the rest of the year as well. Be sure to bring along plenty of water, sunscreen, some insect repellent, and you'll be ready to make the most of a swampy day of hiking.