What is heat exhaustion?
As we get hotter, our blood vessels open up, which lowers blood pressure.
This means the heart has to work harder in order to circulate blood, causing milder symptoms like swollen feat or heat rash.
It also affects our levels of fluids and salt through sweating, and alters the balance of them in our bodies.
When this is combined with decreased blood pressure, heat exhaustion can result.
The symptoms include nausea, dizziness, muscle weakness, sweating, cool and clammy skin, irritability and confusion.
A key sign is body temperature going above 41C – which can occur within 10 to 15 minutes of being in hot weather, according to the Centre for Disease Control and Prevention.