Heading Outdoors in Extreme Heat? Pharmacists Share Tips to Prevent Dehydration and Heat Exhaustion

Recently, a delivery rider walked into the pharmacy during the hottest part of the afternoon. He had been on the road for hours. Although he had been drinking water, he still felt weak, had a pounding headache, and said he felt as if he was “moving through mud.”

This is a pattern pharmacists see quite often during very hot weather. People may think they are doing enough by sipping water, but heavy sweating can cause the body to lose both fluid and important electrolytes such as sodium and chloride. When these losses accumulate, the body may struggle to maintain normal circulation, muscle function, and temperature regulation.

 

Why Hot Weather Can Be a Dehydration Trap

Sweating is the body’s natural cooling system. It helps lower body temperature, but it also causes water and salt loss. In high heat, especially during outdoor work, sports, long walks, or delivery riding, this loss can happen faster than many people realise. Heat exhaustion is commonly associated with excessive water and salt loss through sweating. 

This is why some people say, “I drank water all day, but I still feel terrible.” Water helps replace fluid volume, but after prolonged sweating, the body may also need electrolytes. In some situations, drinking large amounts of plain water without replacing electrolytes can worsen an imbalance and contribute to low sodium levels. 

What Symptoms Should You Watch For?

Common warning signs of heat exhaustion include headache, dizziness, weakness, thirst, nausea, heavy sweating, reduced urine output, and muscle cramps. These symptoms should not be ignored, especially if they develop after time in the sun or after physical exertion. 

Seek urgent medical care immediately if the person becomes confused, collapses, has a seizure, stops sweating, or feels very hot with worsening symptoms. Those features may suggest a more serious heat-related emergency.

 

Who Should Be Extra Careful?

Some groups are at higher risk of dehydration and heat-related illness:

Outdoor workers and athletes are at especially high risk because they may sweat heavily for long periods. Older adults are also more vulnerable because their thirst sensation and temperature regulation can become less effective with age. Certain medicines can increase the risk, including diuretics and other medicines that affect fluid balance or how the body responds to heat. Asking a pharmacist whether your regular medicines require extra precautions in hot weather is a sensible step. 

 

ORS, Isotonic Drinks, or Plain Water: What Should You Choose?

For mild daily fluid replacement, plain water remains the preferred option. But if someone has been sweating heavily for hours and is starting to feel unwell, an oral rehydration solution or oral rehydration salts may be more suitable, as they are designed to replace both fluids and electrolytes in a balanced way. WHO guidance describes ORS as a glucose-electrolyte solution used to treat dehydration, and WHO heat-health guidance notes that oral rehydration with electrolytes may be needed in heat illness. 

Isotonic drinks can help replenish some electrolytes, but they are generally formulated more for exercise recovery than for medical rehydration. They may also contain more sugar, and carbonated versions may make some people feel nauseated or cause heat-related stomach upset. Standard soft drinks and high-caffeine drinks are not ideal choices when someone is already dehydrated. 

A practical message is this: if you have only been outdoors briefly and feel well, water may be enough. If you have been sweating heavily and have symptoms such as cramps, dizziness, marked fatigue, or headache, consider electrolyte replacement and speak to a pharmacist, especially if symptoms are not improving.

Practical Tips from Pharmacists

Drink early, not only when you feel thirsty. Thirst can be a late sign that mild dehydration has already started. Take small, regular sips during the day rather than waiting until you feel exhausted. 

If you need to be outdoors, try to reduce direct sun exposure during the hottest hours, rest in shaded or cool areas, and wear light clothing. For those doing physical work outdoors, planning hydration breaks is just as important as carrying a bottle.

If you take regular medicines for blood pressure, fluid retention, allergies, or other chronic conditions, check with your pharmacist whether hot weather changes how you should manage fluids or monitor symptoms. Do not stop prescribed medicines on your own, but do ask whether you need extra precautions.

Final Message

Extreme heat can affect anyone, but it is especially risky for people who work outdoors, exercise in the sun, are older, or take medicines that affect hydration. The earlier dehydration and heat exhaustion are recognised, the easier they are to manage safely. Community pharmacists are well placed to help the public identify early warning signs, choose suitable rehydration options, and decide when further medical care is needed.

 

 

 

 

References

Centers for Disease Control and Prevention. (2025, April 23). Heat and cold illness in travelers. In CDC Yellow Book. https://www.cdc.gov/yellow-book/hcp/environmental-hazards-risks/heat-and-cold-illness-in-travelers.html 

Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. (2026, March 3). Heat-related illnesses. https://www.cdc.gov/niosh/heat-stress/about/illnesses.html 

Mid and South Essex Integrated Care System. (2025, October 13). Summer health advice. https://www.midandsouthessex.ics.nhs.uk/health/summer-health/ 

World Health Organization. (2006). Oral rehydration salts: Production of the new ORS (WHO/FCH/CAH/06.1). https://www.who.int/publications/i/item/WHO-FCH-CAH-06.1 

World Health Organization. (2011). Public health advice on preventing health effects of heat: New and updated information for different audiences.