There are many causes of headaches. However, in specific conditions, a headache is a symptom of what your body is trying to tell you it needs.¹ Dehydration during hot weather conditions, intense physical activity or even whilst taking specific medications can quickly lead to more severe conditions developing. Heat exhaustion occurs when the body cannot cool itself down if the body temperature rises too quickly, either in response to the environment or other factors. Heat exhaustion and headaches are closely linked because dehydration is known to cause headaches, and dehydration happens in hot weather.

Definition of heat exhaustion

• Heat exhaustion is when someone gets too hot, too quickly. In an attempt to cool itself, you may sweat more, which can result in a loss of fluid and dehydration, leading to other heat-related illnesses
• Heat-related illnesses include heat cramps, heat stroke and heat exhaustion
• Heat exhaustion, heat cramps, and heat stroke are differentiated by their symptoms

Heat exhaustion symptoms

• Clammy skin
• Tiredness
• Muscle cramps 
• Dizziness
• Vomitting
• Sweating
• Weak or fast pulse
• Headache 
• Fainting 

Heat cramps

• Muscle cramps/spasms in the abdomen or leg

Heat stroke

• Dizziness
• Nausea
• Damp skin
• Fainting
• Headaches
• Fast and strong pulse
• Temperature above 37℃
• Loss of consciousness

Importance of recognising symptoms early

• If heat exhaustion is not recognised early and treated appropriately it may lead to heat stroke, which can be fatal²
• Headaches are usually an indicator of dehydration and a need for fluid in heat exhaustion

Overview of heat exhaustion

Causes of heat exhaustion

• Long periods of exposure to a high-temperature environment
• Intense physical exertion or labour in hot environments
• Dehydration and not consuming enough fluids in the above circumstances

Common symptoms

• Increased sweating 
• Dizziness
• Nausea
• Muscle cramps
• Intense headaches
• Heat rashes - red spots presenting on the abdomen, especially in children³

Mechanisms linking heat exhaustion and headaches

Headaches are associated with heat exhaustion for the following reasons:

• Dehydration
• Loss of fluids without replacement 
• Loss of electrolytes
• Constricted blood vessels due to dehydration which reduces blood flow.
• Pain receptors in the brain become activated

Overheating and vasodilation (blood vessels become wider)

• Blood vessels become wider to reduce heat
• Wider blood vessels increase the pressure in the brain, which can cause headaches

Stress response

• Hormones can also cause headaches, especially in response to stressful situations
• These stress-associated headaches are known as tension-type headaches

Exertion and metabolic stress

• Strenuous physical activity can also cause headaches
• Physical activity means sweating, which results in a loss of fluids, which can lead to headaches

Risk factors

Environmental factors

• Living and work areas that lack good ventilation and have high humidity can cause heat exhaustion, leading to headaches
• Lack of shade, such as in high population density areas, such as the urban environment, where there is less shade

Individual factors

• Medication that affects blood circulation or causes dehydration 
• Age (elderly and young children are at greater risk of factors that lead to headaches)
• Medical conditions that disrupt the ability to thermoregulate

Occupation hazard

• Occupations that require intense and prolonged physical activity such as military personnel, construction workers, factory workers, and miners are at risk of heat exhaustion⁴

Prevention strategies

Hydration

• Being aware of hot weather and keeping hydrated or increasing fluid intake 
• Replenishing electrolytes lost through sweat via electrolyte replenishing drinks if necessary⁵

Managing exposure to heat

• Avoid being outside in peak heat hours like the midday sun
• Dressing appropriately during hot weather - light, breathable clothing that facilitates cooling 

Awareness of early heat exhaustion symptoms

• Monitor signs of the developing headaches, like light sensitivity, pain and fatigue
• Being proactive and taking immediate action to resolve dehydration by proper hydration and increasing fluid intake

Treatment and management

Rapid intervention

• Cool environments - fan, aircon or high ventilation areas 
• Increased fluid intake (water) 
• Avoid foods that cause dehydration (salty foods, caffeine, etc)
• Awareness of various cooling techniques (like cold compress)

When to seek medical attention

• Long-lasting and persistent headaches, even with intervention, is a good sign that medical attention is needed
• The development of severe symptoms like fainting and pain

Summarry

• Awareness and prevention are key in avoiding headaches associated with heat exhaustion
• Increasing fluids during hot weather, intense physical activities and in specific medical conditions can prevent worsening of symptoms