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33 signs of dehydration to look out for

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Should you experience dehydration – that is, your body loses more fluids than you take in, you’re likely to see signs of dehydration and, if left untreated, severe dehydration symptoms. Below, we explore what symptoms fall into the different categories of dehydration, when you can try and rehydrate yourself and when you must seek medical advice. 

Signs of mild-to-moderate chronic dehydration 

‘Dehydration’ can be seen on a spectrum with ‘mild’, ‘moderate’ and ‘severe’ dehydration being terms used to describe how dehydrated a person can be. Meanwhile, ‘chronic’ and ‘acute’ refer to how quickly the dehydration symptoms occur.  

The chances are, most people experience chronic (ongoing) mild to moderate dehydration regularly. When the usual amount of water in your body decreases, it disrupts the harmony of your minerals, for example, mineral salts, such as electrolytes and sugar like glucose. Electrolytes are examples of solutes (substances that usually dissolve in your blood) that help transport nutrients into your cells, remove waste products out of them and control your acidity and pH levels. Examples include sodium, potassium, chloride, magnesium, calcium, phosphate, and bicarbonates. It’s easy to see why an imbalance of minerals can prevent your body from working optimally, contributing to some of the dehydration symptoms described below.  

Early warning signs of mild-to-moderate chronic dehydration include:  

1. Feelings of thirst 

2. Having a dry mouth, lips or tongue  

3. Dizzy or lightheaded sensations – especially when you stand up after sitting or lying down. If this comes and goes after a few seconds, it can be considered ‘mild-to-moderate’ dehydration. Notably, there could be other reasons for these sensations outside dehydration.   

4. Feeling tired 

5. Urinating less regularly than what’s normal for you – When you’re dehydrated, the amount of blood circulating around your body (your blood volume) decreases. Reduced blood flow around your body and to your kidneys causes them to keep as much fluid as possible, resulting in you urinating less often.

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In the event that you have untreated diabetes, you may have lots of sugar in your blood, forcing your kidneys to work doubly hard to filter and absorb the excess. When your kidneys can’t keep pace, you feel the urge to urinate more to remove the extra sugar, extracting fluids from your tissues as you do so. This can make you dehydrated. If you’re feeling thirsty despite drinking a lot of water and are urinating more than what is usual for you, contact your GP. If you’re already diagnosed with diabetes and experiencing excessive urination and thirst, seek urgent medical attention.

6. Constipation – When your body lacks water, it can make your stools harder and therefore more difficult to pass.  

7. Muscle weakness – dehydration can result in diminished strength and stamina. 

8. You’ve lost your appetite – In a study of people aged 65+ receiving home health care, dehydration was associated with a decreased appetite, although the researchers noted that the causal relationships between dehydration, depression, appetite, and physical performance needed to be further investigated. However, appetite loss been cited as a possible sign of mild dehydration in all adults

9. Dehydrated skin – This can happen when there’s not enough water in your skin and can occur in anyone, no matter if they have oily, dry or combination type skin. This is different from dry skin, which is a skin type and where the complexion lacks oils and looks more flaky and dry as a result. With dehydrated skin, you may spot itchiness, dullness, increased sensitivity to wrinkles and fine lines, dry mucous membranes, for example in your nose, and / or darker circles beneath your eyes. If your skin becomes dryer over time (rather than always being dry) it could be a sign of dehydration.   

10. Headaches – As well as provoking headaches, dehydration can also worsen underlying medical conditions, such as cerebrospinal fluid (CSF) hypotension.  

11. An exaggerated response to pain – The participants in a small study of healthy men experienced more pain when their upper or lower arms or legs were immersed in cold water (a cold pressor test) when they were dehydrated compared to when they had good hydration. Meanwhile, the dehydrated participants of another small study had the pain networks in their brain activated more and a reduced pain threshold when they encountered the cold pressor test compared to when they were rehydrated. 

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If you have highly calibrated biometric weighing scales with a body water measurement feature, you may notice your body weight drops slightly each day. This could be a sign of dehydration.

If you’re experiencing any of the above, drink ample amounts of fluids, such as water or herbal, non-caffeinated tea. Oral rehydration solutions and salts available from pharmacies can often aid with moderate dehydration as they help optimise the amount of fluid your body can take in.

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Where the signs of dehydration outlined above persist, even after you’ve tried drinking more fluids and oral rehydration solutions, contact your GP.

Who’s most at risk of dehydration?

  • Babies and toddlers as, due to their low body weight, they’re sensitive to even tiny amounts of water loss.

  • Older people because they can be less aware that they’re developing dehydration and that they should keep drinking.
  • People living with long-term health conditions, for instance diabetes or alcoholism.
  • Potentially athletes who can, through exercising for long periods, sweat out significant amounts of body fluid. 
  • Those who have been exposed to hot temperatures for a considerable amount of time, especially without access to fluids.
  • Individuals who have recently been vomiting, had diarrhoea or sun stoke.    

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In cases where you or someone you know fits into the above ‘at risk’ categories and are experiencing signs of dehydration, you / they must access medical help quicker.

Dehydration symptoms in babies and children include:

1. Being less active than usual 

2. Feeling drowsy 

3. Having a dry mouth 

4. Fast breathing 

5. Hands and feet that appear cold and blotchy 

6. Crying without tears 

7. Having a sunken or soft area on top of a baby’s head 

8. Having sunken eyes – The fragile skin beneath the eyes may appear dark, sunken, hollow, or thin or may have a dark shadow over their lower eyelid or dark circles under their eyes. This could cumulate in their face looking tired overall. 

9. Producing fewer wet nappies, or nappies that are lighter than normal (in older children this may appear as them weeing less often). 

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These could all be signs of worsening and severe dehydration in your child. If these signs are present, especially in the context of other illness, such as vomiting, fever or diarrhoea, please seek urgent medical advice via your GP, calling the NHS’ 111 helpline or A&E. Contact your GP, out of hours service, or NHS by calling 111 immediately if your baby has had six or more bouts of diarrhoea in the past 24 hours, or if they’ve thrown up three times or more in the past 24 hours.

What are the signs of severe acute dehydration?

Severe dehydration symptoms in both adults and children can include:

1. Experiencing extreme tiredness, more than usual and a total lack of energy – Interestingly, in a review that assessed the predictors of dehydration in the elderly, fatigue was one of only two factors that predicted a dehydration diagnosis. There can be other causes of exhaustion but, if you think you’re dehydrated due to other signs, or if you have another illness, such as vomiting, diarrhoea or heat stroke, it could be a severe dehydration symptom.  

2. Feeling extremely thirsty 

3. Having sunken eyes – As with children, the fragile skin beneath your eyes may look dark, sunken, hollow, or thin. Alternatively, you may have a dark shadow over your lower eyelid or dark circles or beneath your eyes. All these could contribute to your face looking tired overall. 

4. Your pee is dark yellow and smells strong – The concentration of particles like chemicals in your bodily fluids like your urine is higher when you’re dehydrated. This increases the likelihood of these chemicals generating a strong smell. When the ratio of water to chemicals in your urine is higher i.e., your well hydrated, the water naturally dilutes the smell and chemicals.

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Even if your urine looks hydrated (pale), it isn’t a sign you can use on its own to determine your hydration status, as your cells might be dehydrated. Alternatively, you might be losing water due to high solute concentrations in your blood, for example if you have diabetes. Therefore, only use this as a sign of optimal hydration if you’re not experiencing any of the other signs outlined here.

5. You’ve not urinated for eight hours or more. 

6. Having a faster heart rate – This severe dehydration symptom can depend on context. For example, if you’ve recently had diarrhoea, this can be more indicative of dehydration. When your blood volume to decreases, your heart beats more rapidly to compensate, prompting your heart rate and blood pressure to rise. Research on whether dehydration causes hypertension (high blood pressure) is limited. However, it’s clear the hormone vasopressin, which is released when your blood volume is low or you have too many dissolved particles in your blood, can trigger the narrowing of your blood vessels, resulting in a blood pressure rise.  

7. Breathing rapidly – As your heart rate increases, so too does your breathing rate.  

8. A slow capillary refill – Making sure you’re not wearing any finger rings or nail polish, pressing down on your nail bed until it turns white should see the colour return in three seconds or less when you stop pressing. If colour takes longer to return, it may indicate you’re dehydrated. This is because the capillary refill test examines the amount of blood flowing through your smallest blood vessels (capillary) and, as we mentioned above, dehydration can reduce the amount of blood circulating around your body. 

9. Dizzy or lightheaded sensations – A low blood volume can also spark low blood pressure. When your blood pressure dips, organs like your brain don’t receive enough oxygen and nutrients usually carried by your blood. The result is light headedness, as if you may faint. If these dizzy feelings when you stand up don’t go away after a few seconds, it could be classed as a severe dehydration symptom.   

10. Feeling confused or delirious 

11. Displaying a low level of consciousness  

12. Having fits (seizures) – A seizure is where a person becomes stiff, loses consciousness and their arms and legs start to twitch. Seizures are emergencies that need to be dealt with urgently. You can find out what to do if someone has a seizure, including putting them in the recovery position, and when to call an ambulance here.  

13. A high core body temperature – Being dehydrated can affect your body’s ability to regulate temperature. When your body temperature rises, you usually sweat to cool down. Yet, when you’re dehydrated, you sweat less, meaning less heat loss and a diminished ability to cool your body down.   

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It’s worth noting that the above dehydration symptoms and signs don’t necessarily accurately diagnose you with dehydration, especially in older adults. This is because context is important when making a diagnosis. The above is also not an exhaustive list of dehydration symptoms.

If you suspect you or someone you know, including an elderly person, is dehydrated, contact your GP, who’ll be able to carry out more accurate tests. Contact your GP, out of hours service, or NHS by calling 111 immediately if you or someone you know is experiencing the above signs of severe acute dehydration, particularly if they’ve recently suffered vomiting, diarrhoea heatstroke or have been unwell.

An infographic in 3 sections. The first section is blue and titled: 'Signs of mild-to-moderate chronic dehydration' with the following listed under an illustrative icon: Thirst, Dry mouth, lips or tongue, Dizzy or lightheaded sensations, Urinating less regularly than normal, Reduced appetite, Dehydrated skin, Headaches, An exaggerated pain response, Constipation, Muscle weakness, Feeling tired. The second section is pink and titled: 'Signs of severe acute dehydration' with the following listed below representative icons: Extreme tiredness, Extreme thirst, Sunken eyes, Dark yellow strong smelling pee, Not Urinating in eight or more hours, Breathing rapidly, A slow capillary refill, Dizzy or lightheaded sensations, Confusion or delirium, A low level of consciousness, A faster heart rate, Fits (seizures), a high core temperature. The third section is yellow and titled: 'Signs of dehydration in children and babies' with the following below illustrative icons: Less active than usual, Drowsiness, Dry mouth, Fast breathing, Cold and blotchy hands and feet, Crying without tears, A sunken or soft area on top of a baby's head, Sunken eyes, Producing fewer wet nappies or lighter than normal.

For tips on how to nourish your body and mind beyond hydration, download the Evergreen Life app, bursting with content to medically reviewed by GPs and wellness experts. 

Reviewed by:

Anna Keeble MA BA Head of Content and Wellbeing Expert

Dr Claire Marie Thomas MRCGP DFSRH DTMH DipNLP MBChB BMedSci Medical Expert

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Jayna Shepherd

Jayna Shepherd is a Content Writer at Evergreen Life. As a BA Journalism graduate, Jayna enjoys the challenge of learning about cutting-edge wellness research and translating that into digestible, chatty plain-English to benefit our app users and content readers.