Water retention happens when your body holds onto fluid that would normally be filtered out through your kidneys. The most common triggers are eating too much sodium, hormonal shifts, sitting or standing for long periods, and certain medications. In most cases, the puffiness is temporary and harmless, but persistent or sudden swelling can signal something more serious.
How Sodium Traps Water in Your Body
Sodium is the single biggest dietary driver of water retention. Your body works hard to keep sodium concentration in your blood within a narrow range. When you eat a salty meal, sodium levels in the fluid surrounding your cells rise. Water follows sodium through a process called osmosis: it moves toward the higher concentration of sodium to dilute it back to normal. This pulls water out of your cells and into the spaces between them, which is what creates that puffy, bloated feeling.
Your kidneys are the main control center for this process. When sodium levels climb, your kidneys slow down sodium excretion to maintain balance, and water gets retained along with it. Total body water and the volume of fluid outside your cells are directly dependent on total body sodium. That’s why cutting back on salt is one of the fastest ways to reduce water weight. The World Health Organization recommends keeping sodium under 2,000 mg per day (about a teaspoon of table salt), though most people in Western countries consume well above that.
Hormones That Tell Your Kidneys to Hold Water
Several hormones regulate how much fluid your body keeps or releases, and when they shift, you notice.
Aldosterone is produced by your adrenal glands and tells your kidneys to reabsorb sodium back into your bloodstream instead of letting it leave through urine. When sodium stays, water follows. Blood volume goes up, and so does that swollen feeling in your hands, feet, or belly. A second hormone, antidiuretic hormone (ADH), works alongside aldosterone. ADH increases the permeability of your kidney’s collecting ducts so water gets reabsorbed without sodium, producing more concentrated urine and keeping extra fluid in your body.
Cortisol, the stress hormone, also plays a role. Prolonged stress or medical conditions that elevate cortisol can promote sodium retention, which in turn holds water. This is one reason people under chronic stress sometimes notice facial puffiness or swollen ankles that seem to come from nowhere.
Why You Retain Water Before Your Period
Fluid retention tied to the menstrual cycle typically peaks in the late luteal phase, roughly days 26 to 27 of a typical cycle, just before menstruation begins. Research published in the American Heart Association journal Hypertension found that women with premenstrual symptoms had exaggerated increases in both renin (a kidney enzyme) and aldosterone during this phase compared to women without PMS.
The mechanism involves progesterone. High progesterone levels increase capillary permeability, essentially making tiny blood vessels leakier. Fluid and proteins seep out of the bloodstream and into surrounding tissue, causing swelling. Progesterone also appears to directly stimulate aldosterone release from the adrenal glands, compounding the effect. In the study, progesterone levels correlated strongly with levels of both renin and aldosterone. Once menstruation starts and hormone levels drop, the extra fluid clears within a day or two. Ankle swelling and breast tenderness were reported in all PMS participants during this late luteal window.
Carbohydrates and Glycogen Storage
Carbs don’t just provide energy. They also carry water. When your body stores carbohydrates as glycogen in your muscles and liver, each gram of glycogen binds roughly 3 to 4 grams of water. This is why people on low-carb or ketogenic diets often lose several pounds in the first week. That initial drop is almost entirely water being released as glycogen stores deplete.
The reverse is also true. A high-carb meal after a period of restriction can cause a noticeable jump on the scale as your muscles restock glycogen and pull water in with it. This isn’t fat gain. It’s fluid shifting in and out of storage, and it stabilizes once your eating patterns even out.
Gravity and Prolonged Sitting or Standing
Spending hours in one position lets gravity do its work on your circulatory system. In a standing person, blood pressure at the feet is roughly double what it is at the heart. That increased pressure pushes fluid out of blood vessels and into the surrounding tissue, especially in the ankles and lower legs. Long flights, desk jobs, and standing shifts all create this effect.
The fix is movement. Your calf muscles act as pumps that push blood back up toward the heart. Walking, flexing your ankles, or elevating your legs periodically helps counteract the hydrostatic pressure that builds up during the day. Compression socks work on the same principle by squeezing the tissue and preventing fluid from pooling.
Medications That Cause Swelling
Several common drug classes promote fluid retention as a side effect. Calcium channel blockers, frequently prescribed for high blood pressure, are among the most likely culprits. The swelling occurs because these drugs relax blood vessel walls, which increases pressure in the small capillaries and pushes fluid into surrounding tissue. Nearly half of people taking this class of medication experience some degree of ankle or foot swelling.
Other medications linked to water retention include:
- NSAIDs (ibuprofen, naproxen) reduce the kidneys’ ability to excrete sodium
- Corticosteroids (prednisone, hydrocortisone) mimic the effects of cortisol and promote sodium retention
- Hormone therapies containing estrogen, progesterone, or testosterone
If you notice new or worsening swelling after starting a medication, your prescriber can often adjust the dose or switch to an alternative.
When Water Retention Signals a Bigger Problem
Most water retention is benign and fluctuates day to day. But certain patterns point to underlying conditions that need attention.
Heart failure causes fluid backup when the heart can’t pump efficiently. Blood pools in the lower extremities, leading to swelling in the legs, ankles, and feet. Fluid can also accumulate in the abdomen or lungs. Swelling in the lungs, called pulmonary edema, causes shortness of breath and requires immediate medical care. Chest pain, an irregular heartbeat, or sudden difficulty breathing alongside swelling are red flags.
Kidney disease impairs the body’s ability to filter excess sodium and fluid. The swelling tends to show up in the legs and around the eyes. When the kidneys lose protein through damaged filtering vessels, the blood’s ability to hold onto fluid drops, and water leaks into tissue even more readily.
Hypothyroidism causes a distinct type of swelling called myxedema, which looks different from typical water retention. The skin becomes dry and thick, particularly around the eyes, with a yellowish discoloration over the knees, elbows, and palms. Unlike most fluid retention, pressing on the swollen area doesn’t leave an indentation.
Pitting vs. Non-Pitting Edema
A simple way to assess swelling at home is the press test. Push a finger firmly into the swollen area for a few seconds and release. If an indentation lingers, that’s pitting edema, and it typically means the fluid in the tissue has a low protein concentration. This type is associated with excess sodium intake, heart failure, blood clots, and vein problems.
If the skin bounces back immediately with no dent, that’s non-pitting edema. This pattern is more common with lymphedema (a blockage in the lymphatic drainage system), lipedema (abnormal fat distribution), or the myxedema seen with thyroid disorders. Non-pitting edema generally requires different management than the pitting variety, so the distinction matters when sorting out the cause.