Symptoms of dehydration depend on its stage: in mild dehydration, you may be barely aware of any trouble, while in severe dehydration you can experience disabling fatigue and excrete only small amounts of brown urine.
Chart 1. Symptoms and Signs of Dehydration in Adults
|MILD Dehydration (1-3% loss of body weight)|
MODERATE Dehydration (4-6% loss of body weight)
SEVERE Dehydration (>6% loss of body weight)
Chart 1. *Skin turgor refers to the time in which the skin recoils after being pinched and released. **Capillary refill time is the time in which a nail regains its normal pink color after being pressed for few seconds. References: 1,24,25
I. Mild Dehydration (Early Symptoms and Signs)
Dehydration in adults is considered mild when it results in a loss of 1-3% of body weight.
Decreased Urination and Strong Yellow Urine
A combination of decreased frequency of urination by day, a decreased volume of the excreted urine in the morning and urine darker than usually are typical early symptoms of dehydration .
Thirst is a typical but unreliable symptom of dehydration. Thirst usually appears after a water loss that results in a loss of 2% or more body weight .
You can be dehydrated and may or may not be thirsty. Older people and children are often less aware of thirst. Also, when you do not eat and drink for several hours or days (due to fasting or starving) and therefore consume no salt, you may feel no thirst.
On the other hand, you may not be dehydrated but can feel thirst because of dry mouth (see below), eating salty food, seeing an attractive drink or from psychological reasons (psychogenic polydipsia).
Some people experience thirst similar to hunger, so when thirsty, instead of drinking, they start to eat . Drinking enough water may, therefore, decrease craving for food.
Dry mouth is an early but unreliable symptom of dehydration.
You can be dehydrated but have moist mouth due to increased salivation when thinking about food.
You can be normally hydrated but having dry mouth due to dry air, breathing through the mouth, anxiety and other strong emotions, drinking alcohol or taking medicines and in conditions, such as inflammation of the parotid glands or Sjögren’s syndrome.
When you are dehydrated, the volume of the blood decreases, which triggers the release of the hormone epinephrine (adrenaline) from the adrenal glands, which constricts the arteries and stimulates the heart in order to maintain the normal blood pressure. You can experience this heart stimulation as pounding heart.
Other Symptoms of Mild Dehydration
- Slight tiredness, lack of energy
- Slight anxiousness, especially in women
- Decreased or increased appetite
- Mild headache
- Reference: 
First Warning Clinical Signs
Clinical signs are abnormalities that a doctor finds during a physical examination.
- Sudden loss of weight (within several hours to few days) by 1-3% (1.5-4.6 lbs in a 154 lbs or 0.7-2.1 kg in a 70 kg person) 
- Slightly increased heart rate 
- Prolonged skin turgor (by up to 2 seconds)
II. Moderate Dehydration
Dehydration in adults is considered moderate when it results in a loss of 4-6% of body weight.
In moderate dehydration, you can experience:
- Symptoms described under mild dehydration plus…
- Chapped lips, itchy throat 
- Burning urination, dark yellow, orange or amber urine
- Feeling cold
- Fatigue, dizziness, vertigo, lightheadedness, drowsiness or insomnia, difficulty concentrating, impaired memory 
- Moderate headache
- Poor appetite (anorexia) , nausea, vomiting, morning sickness (in pregnant women)
- Other: depression, anxiety, nervousness (jitters) , sensitivity to light and noise , bad breath (halitosis) 
In moderate dehydration, a doctor commonly finds:
- Sudden loss of 3-6% body weight (4.5-9 lbs in a 154 lbs adult or 2-4 kg in a 70 kg adult) 
- Dry, sunken eyes; dark circles or bags under the eyes due to localized edema
- Prolonged skin turgor (2-10 seconds) 
- Prolonged capillary refill time (2-4 sec) 
- Increased heart rate or tachycardia (>60-100/min)
- Increased breathing rate (>28/min) [1,6]
- Weak arterial pulse 
- Normal blood pressure, which can drop upon raising up (orthostatic hypotension; systolic pressure drop by 10-15%) [1,6]
- Other: low-grade fever 
III. Severe Dehydration
Dehydration in adults is considered severe when it results in a loss of more than 6% of body weight [1,5].
- Symptoms described under mild and moderate dehydration plus…
- Very little or no urination, painful urination, tea-colored or brown urine
- No sweating despite high ambient temperature, dry itchy skin 
- Extreme thirst (or no thirst at all)
- Apathy, lethargy, confusion
- Severe headache or migraine [14,15]
- Fainting, passing out (unconsciousness), coma
- Other possible symptoms: chest pain, lower back (flank) pain in acute kidney failure due to dehydration , problems with eyesight: blurred vision, temporary vision loss (blindness), tingling and numbness in fingertips (due to hyperventilation), irritability, delirium, hallucinations, seizures
- Sudden loss of more than 6% of body weight: more than 9 lbs in a 154 lbs adult (more than 4 kg in a 70 kg adult) 
- Pale, wrinkled, dry and cool skin
- In heat exhaustion and hypovolemic shock: pale, sweaty and cool skin 
- In heat stroke: dry and hot or flushed skin [9,21]
- Prolonged skin turgor (decreased skin elasticity, “skin tenting,” “doughy skin”): from 10 seconds to several minutes [7,8]
- Prolonged capillary refill time: >4 sec 
- In hypovolemic shock: decreased
- In heat exhaustion, heat stroke and infections: increased 
Other effects of severe dehydration:
- Dry mucous membranes (dry mouth), white, yellow or swollen tongue, dry, cracked, chapped lips, swollen tongue 
- Very sunken and dry eyes
- Increased breathing (hyperventilation), decreased breathing (respiratory depression) or difficulty breathing (dyspnea) 
- Very increased heart rate or tachycardia (can exceed 140/min), faint pulse 
- Swollen parotid glands on both sides (parotitis) 
- Blood pressure can be normal or decreased; in hypovolemic shock, systolic pressure may drop under 60 mm Hg 
- Possibly impaired consciousness (somnolence, coma)
Extreme Dehydration and Death
In adults, dehydration that causes a loss of 10-15% of body weight can result in death .
Symptoms That Can Be Associated With Dehydration
- Bloating can be associated with constipation caused by dehydration.
- Stomach pain or cramps can occur in dehydration caused by diarrhea due to food poisoning (gastroenteritis) [19,20].
- A cough can be triggered by dry, scratchy throat.
- Difficulty swallowing can be associated with dry mouth.
- Nosebleeds can occur due to the dry nasal mucosa in severe dehydration.
- Ringing in the ears or tinnitus can appear temporary before fainting in severe dehydration .
- Yawning can be due to lack of sleep due to anxiety caused by dehydration.
Symptoms NOT Typical for Dehydration
In dehydration, urine is yellow or tea colored and sometimes cloudy. The urine that is only cloudy, but not yellow or dark, is not caused by dehydration but, for example, by a high-protein diet, kidney or bladder infection or inflammation or urinary stones.
Blood in Urine (Hematuria)
Blood in the urine can result from the infection, inflammation, cancer or injury of the urinary tract, but less likely from dehydration. However, some athletes may notice blood in the urine, which may be related to dehydration .
Even severe dehydration by itself does not necessary cause calf cramps in endurance athletes [11,12]. Some doctors still believe dehydration in combination with muscle fatigue causes leg cramps or Charley horse(s) .
Eye twitching does not result from dehydration itself but possibly from the accompanied disorders, such as hypokalemia.
Hands shaking (tremors) is also not typical for dehydration.
Red, bloodshot eyes are not typical for dehydration but can result from irritation of dry eyes in severe dehydration.
There seems to be no evidence of dehydration as a cause of swollen uvula (uvulitis).
There is a lack of evidence that dehydration would cause the swelling of the lymph glands in the neck or armpits. It is possible that normal lymph glands are more palpable in dehydration due to shrinkage of the surrounding tissues, though.
The following symptoms are also not typical for dehydration: skin rash, jaundice, leg or knee pain
- Emedicine (Mild, moderate and severe dehydration)
- Nature.com (Exercise performance)
- PubMed (Vasovagal syncope and tinnitus)
- Uconn.edu (Dehydration and mood)
- Mayo Clinic (Dehydration symptoms)
- SC.gov (Dehydration)
- Nejm.org (Skin turgor)
- Emedicine (Skin turgor)
- WebMD (Heat exhaustion and stroke information)
- Childrenshospital.org (Heat stress)
- PubMed (Muscle cramps)
- PubMed (Muscle cramps)
- Cancer.org (Mouth sores)
- PubMed (Migraine triggers)
- PubMed (Migraine)
- PubMed Central (Bad breath or halitosis causes)
- PubMed Central (Dehydration and psychological performance)
- PubMed (Heat exhaustion and flushed facial skin)
- PubMed (Dehydration and acute abdominal pain)
- NIH.gov (Food poisoning)
- NIH.gov (Hyperthermia)
- PubMed (Blood in urine)
- PubMed Central (Hunger and thirst)
- Hongjun L, Radiology of Infectious Diseases, Volume 2, p. 78
- Kenefick RW et al, 2011, Dehydration and Rehydration Defense Technical Information Center
- Parotitis UC San Francisco
- Nature.com (Perception of thirst)
- Mayo Clinic (White tongue causes)
- Drugs.com (Acute kidney failure)