Dehydration can manifest as thirstiness, headaches, and dry skin. Drinking water, isotonic sports drinks, or skimmed milk are all ways to rehydrate.

Dehydration is when there is an insufficient volume of water in a person’s body. It can occur due to sweating, illness, diarrhea, vomiting, urinary issues, or not drinking enough water. Dehydration can range from mild to severe. Severe dehydration can become life threatening.

This article looks at what the science says about how to stay hydrated and help prevent dehydration. It also discusses the signs of dehydration and when to speak with a doctor.

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Drinking water is an effective way to hydrate. This is because the body loses water during dehydration. There are various reasons water is a good means of hydration. These include the fact that it will almost always maintain a person’s hydration level in the heat, it is calorie-free, and it is easily accessible for most people.

There are other rehydrating drinks besides water. However, research has shown that fluid volume is the single most important factor when it comes to rehydration, at least following exercise.

In order to rehydrate after exercise, an individual must drink a greater volume of fluid than they lost in sweat. This is because even after exercise has ended, the body continues to dehydrate at an elevated rate for some time.

There are other rehydrating drinks besides water. Some people call them “exercise drinks.” However, it is important to note they may not be suitable for everyone and a person should combine them with a balanced diet and other fluid intake.

These contain ingredients that can aid rehydration. For instance, scientists know that sodium can make drinks more effective in rehydrating people. Additionally, dehydration causes losses of electrolytes as well as water. Some rehydrating drinks contain electrolytes to help replenish the body’s stores of them.

A 2023 study compared the hydration potentials of several non-water drinks. Some contained glucose, others were sugar-free, and others were sugar-free and contained small amounts of amino acids. Although the glucose-based drinks rehydrated better than the sugar-free ones, they did not perform as well as the sugar-free drinks containing the amino acids.

Milk is yet another drink that people can use to rehydrate. According to an older 2014 randomized control trial, skimmed milk is better at rehydrating than water, and than electrolyte- or glucose-containing drinks.

However, it is worth noting that this study had a very small sample size of 38 people. This means its findings may not apply to larger groups of people.

In some cases of severe dehydration, doctors need to administer fluids intravenously. This involves attaching a thin tube to someone’s vein. The tube connects to a quantity of electrolyte-rich water, which makes its way directly into a person’s blood.

According to the National Institutes of Health (NIH), dehydration can manifest in several different ways. A person may experience the following symptoms:

Signs of severe dehydration include:

Severe dehydration can be life threatening.

If an individual is concerned about being dehydrated or has signs of severe dehydration, they should contact a doctor. An individual may also want to seek medical advice if their dehydration may be the result of an underlying health condition. According to a 2022 review, the following conditions can cause dehydration:

The following are some questions people frequently ask about rehydrating.

How long does it take to rehydrate the body?

There is no fixed time for how long this can take. The rehydration process works differently for different people and depends on an individual’s level of dehydration.

What is the fastest way to rehydrate?

Some older evidence suggests that skimmed milk may be better than both water and sports drinks for rehydration. However, this evidence remains limited. Experts need to conduct more research on this topic.

How much water does a person need?

Since everybody is different, there is no universal amount of water that every person has to drink. However, scientists estimate that the average adult should drink between 2–3 liters of water every day.

Dehydration is when someone does not have enough fluids in their body. It can arise due to exercise or medical conditions. Dehydration can cause symptoms that range from thirstiness to fainting. When it becomes severe, dehydration can be life threatening.

The most important aspect of rehydration is to drink enough fluids. Another important rehydration tip is to drink beverages that have added sodium, such as isotonic sports drinks. Research suggests that the most rehydrating of these drinks are sugar-free but contain small amounts of amino acids. These amino acids can improve hydration. However, these may not be suitable for everyone and a person should be sure to drink other other fluids as well.

There is some limited evidence that drinking skimmed milk provides better hydration than drinking either water or sports drinks. Water may be one of the best options for rehydration in most cases.