1) Shed a few layers
Our bodies have cooling all sussed out. When we get hot, we sweat, and as that sweat evaporates it draws heat energy from the skin, cooling us down in the process. So the best way to stay cool if you're out of direct sunlight (and in sympathetic company) is to wear as little as possible.
If you do need to cover up, however, wear loose-fitting clothes that allow air to flow over the skin, speeding up evaporation. Also try to wear light-coloured garments, as these absorb less of the Sun's radiation than darker clothing.
If you're exercising, meanwhile, don some high-tech sportwear that uses 'moisture wicking' fabrics. These fabrics transport sweat away from the skin to the outer layers of the material, where it can spread out and evaporate away.
2) Have a cold drink...
As you sweat, you'll need to replace all that water you're losing. One way to figure out how hydrated you are is to check the colour of your urine. If it's light like lemonade, then you're probably fine; if it's dark like apple juice then you're dehydrated.
When you become dehydrated, the body slows down its sweat rate to conserve fluid, making you even hotter. So a cold drink can rehydrate you and help you cool down.
But while an ice cold cider may seem like a good idea, alcohol is actually a diuretic (it causes you to pee more), which can make you dehydrated. It also causes the blood vessels in your skin to dilate, making you feel hotter. So if you want to stay cool, go easy on the booze.
3) Don't open all the windows
To create a refreshing breeze on a stifling summer's day, don't haphazardly throw open the windows. Instead, generate a draught by opening downstairs windows that are in the shade, and upstairs windows that are in the Sun.
Because hot air rises, sunny upstairs rooms will be warmer than those that are downstairs in the shade. This sets up a pressure difference, and by strategically opening windows in these rooms you'll create a breeze that draws in cool, fresh air from downstairs and forces warm air out of the house. You can increase this effect by using window-mounted fans to suck in air downstairs and blow out air upstairs.
How do you keep cool in the Sun? Do you have any other tips? Let us know on Twitter.