When you have heat intolerance, it’s often because your body isn’t regulating its temperature properly. Your body regulates its temperature by maintaining a delicate balance between hot and cold.
The hypothalamus is a part of the brain that regulates your body’s temperature. When you get too hot, your hypothalamus sends a signal through your nerves to your skin, telling it to increase sweat production. When sweat evaporates off of your skin, it cools your body down.