Some diseases can leave adults dehydrated, robbing your body of the fluids it needs to work right—and making it harder to protect your heart, kidneys, and more. Conditions like diabetes, Sjögren’s disease, and digestive issues (think celiac disease) can either mess with how your body handles fluids or cause vomiting/diarrhea that leads to fluid loss.
1. Celiac Disease
Celiac disease is a long-term autoimmune issue that damages your small intestine. It happens when you eat gluten—a protein in wheat, rye, barley, and some other grains. Treatment means sticking to a gluten-free diet.
When the tiny, finger-like villi lining your small intestine get damaged from celiac, it raises your risk of not absorbing nutrients well (called malabsorption). Diarrhea is super common with this, and that can lead to dehydration. In rare cases, some people with celiac get “celiac crisis”—severe diarrhea that causes dangerous dehydration, weight loss, and messed-up body chemistry.
Symptoms of celiac can vary a lot—some people don’t even notice them. But when they pop up, adults might have:
- Stomach pain
- Bloating
- Long-term diarrhea
- Constipation
- Gas
- Lactose intolerance
- Loose, bulky, greasy, stinky stools
- Nausea
- Vomiting
2. Sjögren’s Disease
Sjögren’s disease (previously known as Sjögren’s syndrome) is a chronic autoimmune disorder that affects your whole body. It causes problems when your immune system attacks the glands and tissues that make moisture—like your salivary glands and the moist linings in your mouth or nose.
Dehydration can happen because the disease messes with your body’s ability to balance fluids and electrolytes (minerals that help control water levels).
Other symptoms of Sjögren’s include:
- Dry cough
- Dry airways (nose, throat, mouth—called xerostomia)
- Dryness in your digestive tract or vaginal tissues
- Dry eyes (xerophthalmia)
- Dry skin
- Shortness of breath (dyspnea)
- Fatigue
- Joint or muscle pain/weakness
- Numbness or tingling in your hands/feet
- Skin rashes
- Swollen glands in your face/neck
About half of people with Sjögren’s also have another autoimmune connective tissue disease, like lupus, rheumatoid arthritis, or scleroderma. Sometimes, the immune system even attacks other organs, causing damage.
3. Ulcerative Colitis
Ulcerative colitis is a type of inflammatory bowel disease (IBD) that causes inflammation and open sores (ulcers) in the inner lining of your large intestine (colon and rectum). It usually happens because your immune system is overactive.
Dehydration can occur because the inflammation messes with your large intestine’s ability to absorb water and electrolytes (like magnesium, sodium, and potassium). Frequent, watery diarrhea—common with ulcerative colitis—also makes dehydration worse.
Symptoms can range from mild to severe, and many people have “remission” periods where symptoms go away. Besides stomach pain and changes in bowel habits, you might feel:
- Tired and low on energy
- Fever
- Nausea or vomiting
- Unplanned weight loss
4. Cystic Fibrosis (CF)
In people with CF, a gene mutation (in the cystic fibrosis transmembrane conductance regulator, or CFTR, gene) messes up how your body processes chloride (a part of salt).
This makes you lose more sodium than normal, so you’re more likely to get dehydrated—especially when you exercise a lot, get sick, or it’s super hot. The mutation also changes how your thirst works, so you might not drink enough fluids either.
Other symptoms come from thick, sticky mucus (instead of thin, slippery mucus) that gets in the way of organ function. This can lead to:
- Diabetes
- Diarrhea
- Trouble breathing
- Fertility problems
- Frequent lung infections
- Malnutrition
- Pancreatic failure
- Permanent lung damage
- Unplanned weight loss
5. Crohn’s Disease
Crohn’s disease is a chronic inflammatory bowel disease that can affect any part of your digestive tract (but usually hits the small intestine and top of the large intestine). Experts think it might be autoimmune, but the exact cause isn’t clear.
Diarrhea and vomiting from Crohn’s can lead to severe dehydration in some people—if left untreated, this can be life-threatening.
Other symptoms include:
- Stomach pain
- Anemia (low iron)
- Bloating
- Diarrhea (with or without blood)
- Fatigue
- Floating stools (from poor fat digestion)
- Nausea or vomiting
- Loss of appetite
- Unplanned weight loss
6. Diabetes
Diabetes is a chronic disease that messes with your body’s ability to break down glucose (sugar) from food and turn it into energy. It can either interfere with how your pancreas works or how well your body uses insulin.
This leaves too much glucose in your blood (instead of getting to your cells). The extra sugar stresses your kidneys, making you pee more often. When you lose more fluid than you drink, dehydration happens.
Other symptoms of diabetes include:
- Blurry vision
- Constant hunger
- Dry skin
- Fatigue
- More frequent infections than usual
- Frequent urination (often at night)
- Numbness or tingling in your hands/feet
- Excessive thirst (polydipsia)
- Slow-healing sores
- Unplanned weight loss
7. POTS Syndrome
POTS (postural orthostatic tachycardia syndrome) is a blood circulation disorder. It causes low blood pressure or a fast heart rate when you stand up from sitting or lying down.
For up to 10 minutes after standing, you might not get enough blood to your brain—leading to dizziness or lightheadedness. Dehydration can happen because POTS messes with your body’s ability to hold onto fluids.
A common issue is problems with kidney hormones (aldosterone, angiotensin, renin) that control sodium and fluid retention. When there’s not enough fluid in your blood, the low blood volume makes POTS worse.
Other symptoms of POTS include:
- Chest pain
- Coldness or pain in your hands/feet
- Shortness of breath (dyspnea)
- Trouble exercising
- Fatigue
- Headaches
- High levels of plasma norepinephrine when standing
- Nausea
- Reddish-purple legs that go away on their own
- Shaking (tremulousness)
8. Cancer
Cancer happens when some of your body’s cells mutate, grow out of control, and spread to other parts (called metastasis). It can start anywhere in your body. Cancer cells grow and multiply when they shouldn’t, forming tumors (lumps) that are either benign (noncancerous) or malignant (cancerous).
Your fluid needs depend on the type of cancer you have. For example, people with gastrointestinal cancers are more likely to get dehydrated because of nausea, vomiting, diarrhea, or trouble swallowing.
Symptoms vary by where the cancer is, but common ones include:
- Stomach pain
- Changes in bladder function or blood in urine
- Fatigue
- Loss of appetite
- Swelling, lumps, thickening, or other skin changes
- Unplanned weight loss of 10+ pounds
- Unusual bleeding or bruising for no reason
9. Addison’s Disease
Addison’s disease is a rare issue (also called primary adrenal insufficiency or hypocortisolism) where your adrenal glands don’t make enough of the hormones cortisol (and sometimes aldosterone).
Dehydration can be an early sign of Addison’s—linked to low aldosterone levels, which help keep your salt and water balanced.
Addison’s and low cortisol also mess with your body’s ability to handle stress and do normal daily functions.
Other symptoms of Addison’s include:
- Craving salty foods
- Fatigue
- Frequent urination
- Increased thirst
- Irritability or mild depression
- Lethargy (drowsiness or lack of energy)
- Loss of appetite
- Muscle weakness
- Unplanned weight loss
Your adrenal glands sit just above your kidneys. The most common cause is autoimmune adrenalitis—when your immune system attacks the cells in your adrenal glands.
10. Gastroenteritis
Gastroenteritis is a short-term sickness from inflammation of the stomach and intestine linings. It’s often called the “stomach flu,” but it’s caused by noroviruses, other infections, or food poisoning.
Dehydration is the most common problem with gastroenteritis—from fluid and electrolyte loss due to diarrhea and vomiting.
Besides dehydration, symptoms include:
- Stomach pain or cramping
- Nausea or vomiting
- Occasional fever
- Watery diarrhea
11. Hyperthyroidism
Hyperthyroidism is when your thyroid gland is overactive, making too much thyroid hormone. This speeds up your body’s metabolism and processes.
While it might make you feel extra energetic at first, it eventually causes fatigue—your body isn’t meant to work that fast long-term.
Dehydration can be a problem with hyperthyroidism because of high body temperature, sweating, and diarrhea. It can also happen with a “thyroid storm”—a rare but life-threatening issue that causes severe dehydration and heart problems.
Other symptoms of hyperthyroidism include:
- Anxiety
- Heart palpitations
- Increased appetite
- Irregular or fast heartbeat
- Sleep problems
- Unplanned weight loss
12. Sepsis
Sepsis is a life-threatening emergency— a systemic infection that damages vital organs and tissues. It needs immediate medical care.
Dehydration happens with sepsis because of fluid loss from sweating. It also causes internal fluid loss from not drinking enough, fluid leaking out of blood vessels, and sepsis-induced vasodilation (blood vessels widening to get more blood to nutrient-poor areas).
Get medical help right away if you or a loved one has any of these sepsis symptoms:
- Clammy or sweaty skin
- Confusion or disorientation
- Extreme pain or discomfort
- Fever, chills, or feeling very cold
- Fast heart rate and breathing
- Shortness of breath
