What is a good way of staying cool if working outside?

Depends on the conditions and what you need to work on.

Stay hydrated (drink water).

Stay (or at least take breaks) in the shade if you can. Wear sunblock if you can’t.

Wear appropriate clothing.

Wear light colored clothes.

They make neck wraps that you soak in water and then freeze. Those things are amazing at keeping your body temperature under control while working in the heat.

Shade and sweat, motion/breeze. Hydrate.

Hydrate. If working in the sun, wear light colors, and wear a light color hat, preferably with a brim all the way around. If you’re willing to get yourself wet, keep some icepacks and wet towels in the freezer. Every so often, take a washcloth, wrap it around the icepack and stuff it in a pocket. Be warned, it will drip and the washcloth will only do so much. Drape the ice cold (but not stiff…that’s too far) towel around your neck during breaks and such.

Get a cotton T-shirt, your size, get it wet, wring it out and put it on.

Misting systems! Even temporary, portable can make a huge difference!

How do construction workers, and all others like that, work without having to do all that though? What is their secret. They don’t seem to be bothered by the 30 degree C heat all day.

They get used to it after a while.

@chefl, you can kind of get used to it. Sort of, but… If it looks like it’s hot, uncomfortable and dangerous work, it is. When I worked in an outdoor lumber yard I’d sweat all day. I was 18 or 19, in college and it was my job to manually load lumber and concrete for customers who purchased smaller amounts that did not require a forklift. When I got in my car at the end of the day and my clothes finally dried in the AC you could see salt lines all over my shirt. It was exhausting work but by the end of that first summer I was in the best shape of my life. You don’t ever completely get used to that work though.
Through my adult life and now into middle age I have been a cyclist. I can handle hours in 95+ degree heat provided I’m sweating, staying hydrated and don’t stop for too long. The breeze/wind along with sweat makes it almost pleasant as long as you’re not in direct sunlight.

@Blackwater_Park Yeah I guess people can get uses to tons of things. I can see the breeze as you’re cycling makes a lot of difference.

Edited: When we lived in Texas one typically hot summer there was a guy at the local Costco who was dressed as if he was about to step into a blizzard. I asked him what it was all about. He had an insulated suit and had sewed pockets in strategic places (under his hat, the back of his neck, back of the waist, armpits, etc.). It was one of the hottest days of the year and he was as cool as a cucumber because he had ice in cased in plastic Ziploc bags in every pocket.

He said the ice lasted about half hour to 45 minutes depending. He would come to work with a large cooler full of of ice in bags ready to go.

Cooling towel or your neck of forehead. If you have a cooler with you, you can cool the towel back down in the cooler periodically.

Stay in the shade whenever you can, you can bring a parasol if you have your hands free to carry one.

Avoid being out during the hottest part of the day if possible. Usually, 1:00–4:00 more or less in North American in the summer months.

Loose clothing.

Jump into the pool or get wet with the garden hose.

Thin long sleeve cotton shirt. Also, long cotton loose pants that are lightweight. The more skin you protect from the sun the less overheated you will get. I noticed the difference one day when I wore a long sleeve cotton shirt I borrowed from my husband. It kept my arms from overheating in the sun. It has to be light enough to breathe. Now I wear long sleeves in the summer when I’m driving in the car as well. Even with the A/C blowing in the car the sun is harsh and makes my arms feel like they are burning. I can’t stand form-fitting clothing in the summer. I love loose-flowing long dresses or loose-flowing long pants.
I also wear a thin racing cap on my head.
They do sell umbrella hats that can help if you have to stand outside for a long time.
As everyone else said, staying hydrated and resting out of the sun occasionally, and putting a wet towel around your neck or on your head from time to time will help out.

A lot of great ideas.

I was interested in newfangled methods, such as removing sweat glands, it saves heat for a season or two, then they reappear and you can’t abuse it, but if you have a really serious problem, then why not! There are also various special deodorants due to which sweating is reduced, namely, there are special odorless ones! Look and you will be advised in a cosmetics store.

It’s mainly the exhaustion, unable to do anything.

@Pandora That may be good advice if you are in the desert but certainly not areas of high humidity.

@SnipSnip I lived in high humidity, like NC and vacationed in Costa Rica. Still works. It really depends on the material. It has to be very lightweight, loose and breathable material like cotton. For instance, like this.