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Hydration in a nutshell

Dr Roger Henderson
Reviewed by Roger HendersonReviewed on 29.04.2024 | 5 minutes read

Hydration in its simplest form is to supply and retain water in the body's tissues. Take in too little water and you risk dehydration, making it hard for the body to carry out essential functions. And with loss of water, you lose essential salts and minerals, causing further turmoil in your body.

We’ve all experienced mild dehydration at times, like when the weather is hot, or we are doing a sweaty workout. Fighting a fever or a stomach bug also leaves you lacking hydration.

But you might have overlooked the toll a flight can take on your body. An airline cabin draws air in from the upper atmosphere for us to breathe in, and this is very dry. The air cabin can be less humid than the Sahara desert, and you actually lose water through your breath. Telling signs can be a dry feeling in your nose and throat, your contact lenses feeling scratchy, and you might be passing urine less, or it’s dark and strong-smelling.

You might feel thirsty, but this is actually a late sign, as when thirst sets in, your body is already 2% dehydrated. You need to work hard to replace this. Your body will work best if you can plan ahead to avoid dehydration, rather than playing catch-up.

If you’re travelling with little ones, they have a higher body surface area and breathe a bit faster, so they can become dehydrated even more quickly, and salt imbalance follows. It can be tempting to let them snooze through the flight (and give you some peace), but feeling tired and sleepy can also be a sign of dehydration, so make sure they have fuelled up before nodding off.

Doctor’s advice

How can I prevent dehydration?


Dehydration occurs when the body loses more fluid than it takes in, resulting in an imbalance between water intake and water loss. This can happen due to factors such as excessive sweating, vomiting, diarrhoea, fever, or inadequate fluid intake. Dehydration can lead to a range of symptoms, including thirst, dry mouth, dark urine, fatigue, dizziness, headache, and confusion. In severe cases, dehydration can cause electrolyte imbalances, organ dysfunction, and even life-threatening complications. Prompt recognition and treatment of dehydration are essential to restore fluid balance and prevent further health problems.


Rehydration is the process of restoring fluid balance in the body after dehydration has occurred. It involves replenishing lost fluids and electrolytes to re-establish proper hydration levels. Rehydration can be achieved through oral rehydration therapy, which involves drinking fluids containing water, electrolytes (such as sodium and potassium), and carbohydrates to replace lost fluids and nutrients. In cases of severe dehydration or when oral intake is not feasible, intravenous (IV) fluid therapy may be necessary to restore hydration and correct electrolyte imbalances rapidly. Rehydration is essential for reversing the symptoms of dehydration, improving overall well-being, and preventing complications associated with fluid loss.

Other Considerations

In addition to understanding hydration, dehydration, and rehydration, it's important to consider factors that can affect fluid balance and hydration status. These include:

Environmental Conditions

Hot and humid weather, high altitude, and strenuous physical activity can increase fluid loss through sweating, increasing the risk of dehydration. It's crucial to stay hydrated by drinking plenty of fluids and taking breaks to rest and cool down in such conditions.

Medical Conditions

Certain medical conditions, such as diabetes, kidney disease, and gastrointestinal disorders, can affect fluid balance and increase the risk of dehydration. Individuals with these conditions may require special attention to fluid intake and electrolyte management to maintain proper hydration.


Some medications, such as diuretics (water pills), antihistamines, and certain antidepressants, can cause increased urine output or fluid loss, leading to dehydration. It's important to discuss potential side effects with a healthcare provider and take steps to mitigate dehydration risk, such as increasing fluid intake or adjusting medication doses as needed.

Individual Needs

Hydration needs vary depending on factors such as age, gender, body size, activity level, and overall health status. Pregnant or breastfeeding women, older adults, children, athletes, and individuals with certain medical conditions may have unique hydration requirements and should pay close attention to fluid intake to maintain optimal hydration.

Healthwords pharmacists' top tips

When you are losing fluid through a sweaty workout, heatwave or diarrhoea, you are losing more than just water. You are losing important salts such as sodium. If you were to drink simply water, your body would lose most of it, and you would continue to lose the important salts at the same time.

Hypotonic solutions are best for straightforward hydration. These have a lower concentration of salts and sugar than in the body, making them ideal to replace losses. Most oral rehydration solutions or salts fall under this. When taking O.R.S Hydration Tablets, the glucose helps get the sodium that is also included back into the body. This creates a path for water molecules to follow the sodium. It's a game of follow-the-leader back into the body’s cells: glucose first, then sodium, then water.

It’s a win-win to feeling better, as O.R.S side-steps the calories while imitating your body’s natural balance.

Pharmacist recommended products

O.R.S Hydration 3 Flavour Variety: (3 x 24 Soluble tablets) Health Kit
Effective relief for
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Refreshing lemon flavour
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Tasty strawberry flavour
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Fruity blackcurrant flavour
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Recommended by pharmacist
Why this Health Kit

O.R.S are soluble hydration tablets that are specially formulated to replenish drinking water.

They contain a combination of glucose, salts and electrolytes and are suitable for people who lose excess fluid, athletes, and for use in hot climates!

This variety bundle is great for travel and the long summer ahead for the whole family!

When should I see my doctor?

As dehydration becomes more serious, you may feel lethargic and irritable, you may be breathing faster and your heart may be racing, your skin will be dry, cold and less elastic and your eyes may be sunken.

You should seek urgent advice if you have any severe symptoms of dehydration, such as feeling unusually tired or drowsy, if you’re confused or disorientated, or if you have fits or faints, or dizziness when you stand up.

You should also consider seeing your doctor sooner rather than later if you have other medical conditions, such as diabetes, that might make you at higher risk of dehydration than others.

Will dehydration affect my work performance?

It certainly can do - even 1 to 2% of dehydration can have an effect on motor skills and mental performance.

Prevention is better than cure, so plan ahead and remember to keep a bottle of water or hydration solution handy during your shift or meetings, and top up throughout the day. If you think you have mild dehydration, you can top up gradually and this shouldn’t keep you away from work.

Depending on the nature of your work, be cautious – if you are very dehydrated, you may need to postpone work or meetings.

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Dr Roger Henderson
Reviewed by Roger Henderson
Reviewed on 29.04.2024
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