Oral rehydration solutions and electrolyte drinks explained

When the body loses a lot of fluid through diarrhoea, vomiting, sweating or fever, it loses salts and minerals as well as water. Drinking plain water replaces the volume but not the salts. An oral rehydration solution contains measured amounts of sugar and salts, so that the gut can take up water efficiently.

The NHS dehydration page describes them as powders mixed with water that replace the salts and minerals the body has lost, and says pharmacists recommend them. They are sold over the counter as sachets, and some products are available on prescription for certain groups.

The NHS diarrhoea and vomiting page makes fluids the priority, with small sips if you feel nauseated, and says a pharmacist can help, particularly if you notice dark urine or passing less urine. A pharmacist may recommend oral rehydration powders, and may suggest loperamide for short-term relief in adults.

Typical situations for a sachet include a stomach bug, heat exposure with sweating, or fever. Diarrhoea usually stops within 5 to 7 days and vomiting within 1 to 2 days, per the NHS, so for most healthy adults the aim is simply to stay hydrated while it passes.

• Make up sachets exactly as the packet directs, using the stated amount of water.

• Sip steadily rather than gulping.

• Do not add extra sugar, salt or squash to the mixture.

• Keep eating small amounts of plain food when you can.

Many sports and energy drinks are formulated for people exercising, and are often high in sugar. The NHS advises avoiding fruit juice and fizzy drinks when you have diarrhoea and vomiting, which would include sugary soft drinks. Everyday healthy drinks suggested in NHS eating advice include water, lower-fat milk and unsweetened tea or coffee, with 6 to 8 glasses of fluid a day.

Electrolyte tablets and powders for sport vary in composition. They are not designed to treat dehydration from illness in the way that rehydration solutions are, and people with heart, kidney or blood pressure problems, or on salt-restricted diets, should check with a doctor or pharmacist before using products that add a lot of sodium or potassium.

The NHS says babies, children and older adults are at higher risk of becoming dehydrated, as are people with diabetes, those taking diuretics and those who rely on others for drinks. Heat, high fever and alcohol add to the risk.

In babies, signs include a sunken soft spot on the head, fewer wet nappies, few tears when crying, drowsiness or irritability. The NHS says never to dilute baby formula and to continue breast or bottle feeding. Anti-diarrhoea medicine should not be given to children under 12.

In adults and children the NHS lists excessive thirst, dark yellow urine and passing urine less often, dizziness or light-headedness, tiredness, a dry mouth and sunken eyes. Pale urine is a good everyday guide that you are drinking enough.

Prevention is mostly habit: keep up regular drinks, increase them during illness, heat or exercise, and offer drinks and watery foods to anyone who depends on you for them.

The NHS says to call 111 or contact a GP urgently for unusual tiredness, persistent dizziness, dark urine, rapid breathing, or a sunken soft spot in a baby. For diarrhoea and vomiting it also advises 111 if signs of dehydration persist after rehydration sachets, if fluids cannot be kept down, if there is blood in the stool or from the back passage, or if diarrhoea lasts over 7 days or vomiting over 2 days.

Call 999 or go to A&E for pale or cold skin, difficulty breathing, confusion or severe drowsiness, vomiting blood or material like coffee grounds, green or yellow-green vomit, a stiff neck with sensitivity to light, or severe headache or abdominal pain.

Do not use oral rehydration powder to replace medical review in anyone who is very unwell. Follow the packet directions for children and babies, and ask a pharmacist for advice if the person is under the age on the label. Keep unused powder away from children, and make up fresh solution as the instructions say.