Why Does the Body Hold Water? Causes of Oedema and When to Get Help

Short answer: water retention, also called fluid retention or oedema, is swelling caused by fluid building up in body tissues. Long periods sitting or standing, salty food, pregnancy and some medicines are common causes, but swelling can also be linked to a blood clot or problems affecting the heart, kidneys or liver.

What does water retention look like?

Oedema commonly affects the ankles, feet and legs. The area may look puffy, the skin may appear stretched or shiny, and pressing it can sometimes leave a dent. Jewellery, socks or shoes may feel tighter. Swelling can affect one side or both, and that distinction matters.

What commonly causes swollen ankles, feet or legs?

The NHS lists several possible causes:

• sitting or standing in one position for a long time;
• eating too much salty food;
• pregnancy;
• some medicines, including certain blood-pressure medicines, contraceptive pills, hormone therapy, antidepressants and steroids;
• being overweight, varicose veins or thyroid problems;
• an injury, bite or infection;
• problems affecting the kidneys, liver or heart; or
• a blood clot.

Because the causes range from temporary to serious, “puffiness” is not a diagnosis. Do not stop prescribed medicine because you suspect it is contributing; ask the prescriber or a pharmacist.

When should you get medical help?

Call 999

Call 999 if swelling occurs with shortness of breath or difficulty breathing, a tight, heavy or painful chest, coughing up blood, noticeable palpitations, or feeling lightheaded, faint, confused, sick or clammy.

Use NHS 111 or request an urgent GP appointment

Seek urgent help if one ankle, foot or leg is swollen without a known cause; swelling is severe, painful or very sudden; the area is red or hot; swelling is also present in the face or tummy; you have a high temperature or feel shivery; or you have diabetes with swollen feet, ankles or legs.

Make a routine GP appointment

See a GP if swelling in both ankles, feet or legs has not improved after a few days of home care, is getting worse, or you have a diagnosed condition affecting your heart, kidneys or leg veins.

What may ease mild temporary swelling?

For swelling that does not have a warning sign, NHS self-care includes:

• raising the legs or swollen area on a chair or pillows;
• gentle exercise such as walking to support blood flow;
• avoiding long periods sitting or standing still;
• wearing wide, comfortable shoes and avoiding tight socks or clothing; and
• washing, drying and moisturising the feet to help prevent skin problems.

Treatment for swelling that persists depends on its cause. Prescription “water tablets” are medicines used for specific conditions and should not be borrowed or used for cosmetic water loss.

Is period-related puffiness the same as oedema?

Some people notice a temporary change around menstruation, but persistent or severe swelling still deserves assessment. During pregnancy, gradual swelling can be common; a sudden increase in swelling of the face, hands or feet—particularly with a severe headache, visual disturbance, pain below the ribs or feeling very unwell—requires immediate contact with a midwife, GP or labour ward because it can be a sign of pre-eclampsia.

Where do food supplements fit?

A food supplement cannot be advertised as treating oedema. In a formula containing qualifying amounts, magnesium may use the authorised claim that it contributes to normal electrolyte balance, and vitamin B6 may use the authorised claim that it contributes to the regulation of hormonal activity. Those statements do not mean that the product treats swelling or replaces medical care.

Most botanicals in “water-balance” supplements should be compared by their identity, plant part, form and declared amount rather than by treatment claims. Our water-balance ingredient guide explains the label details.

Frequently asked questions

Does drinking less water reduce swelling?

Do not deliberately restrict fluids unless a clinician has told you to do so for a medical condition. Fluid advice depends on the cause of the swelling.

Is a sudden change on the scales body fat?

Short-term weight changes can reflect water, food and normal variation, but weight alone cannot identify the cause of swelling. Do not use rapid “water loss” as a weight-management method.

Can a pharmacist help?

Yes. A pharmacist can check medicines, product warnings and whether symptoms should be referred. For warning signs, use the NHS pathway rather than waiting to see whether a supplement helps.

Sources

• NHS: swollen ankles, feet and legs (oedema)
• NHS: swelling in pregnancy
• Great Britain Nutrition and Health Claims Register

Written by: Barry Lees, founder of The Health Improvers
Last reviewed: 2 August 2026

This guide is general information, not diagnosis or medical advice. Food supplements are not a substitute for a varied, balanced diet and a healthy lifestyle.