Which group is at the highest risk for clinical dehydration?

September 26, 2025 •

4 min read

According to Mayo Clinic, infants, children, and older adults face the greatest risk for clinical dehydration due to various physiological factors. This article explores why certain populations are more vulnerable and offers practical advice to help mitigate these risks.

Quick Summary

Infants, children, and older adults are most susceptible to clinical dehydration due to a combination of physiological and behavioral factors. Diminished thirst sensation, higher fluid needs relative to body weight, and increased fluid loss from illness all contribute to their increased risk.

Key Points

Highest Risk Groups: Infants, young children, and older adults are the populations most susceptible to clinical dehydration due to distinct physiological vulnerabilities.
Infant Vulnerabilities: Infants and young children face higher risks because they lose fluids more rapidly, cannot communicate thirst, and are highly susceptible to fluid loss from illnesses like diarrhea and vomiting.
Older Adult Vulnerabilities: Older adults have a blunted thirst sensation, lower fluid reserves, and often take medications or have chronic conditions that increase dehydration risk.
Signs to Watch For: Key signs of dehydration include dark urine, dry mouth, fatigue, and confusion, though these can differ between age groups.
Prevention is Critical: The best strategy for all at-risk groups is proactive prevention, which involves active monitoring of fluid intake and acting quickly at the first signs of illness or fluid loss.
Chronic Illness Connection: Individuals with chronic diseases like diabetes and kidney disease, as well as athletes and outdoor workers, also face elevated risks of clinical dehydration.

Vulnerable populations: Infants, children, and older adults

For many, staying hydrated is a matter of remembering to drink water. However, for certain demographic groups, the risk of dehydration is significantly higher and more complex. The two primary groups facing the highest risk for clinical dehydration are the very young (infants and children) and the very old (older adults). While the causes and manifestations differ between these age extremes, the consequences of severe dehydration can be life-threatening in both cases. Several factors, from physiological differences to environmental conditions and chronic illnesses, compound their vulnerability.

Why infants and children are especially vulnerable

Infants and young children have a different physiology that puts them at a greater disadvantage when it comes to maintaining proper hydration. Understanding these unique factors is crucial for caregivers.

Higher body surface area to mass ratio: A child's higher surface area compared to their body weight means they lose more fluid through their skin via sweating. This makes them more susceptible to fluid loss, especially in hot weather.
Greater fluid turnover: Children have a higher metabolic rate, which means they use and lose water more quickly. Any illness that causes fluid loss, such as diarrhea, vomiting, or fever, can rapidly lead to dehydration.
Inability to communicate thirst: Young children and infants cannot reliably express that they are thirsty or don't feel well. Caregivers must actively monitor their fluid intake and watch for symptoms of dehydration.
Increased risk during illness: Diarrhea and vomiting are the most common causes of dehydration in young children. High fevers also contribute to rapid fluid loss. During an illness, a child may also have a reduced appetite and refuse to drink, further escalating the risk.

Why older adults face a heightened risk

As people age, natural changes in the body and lifestyle factors increase their susceptibility to dehydration. Many older adults are already starting with a lower total body water percentage compared to younger adults.

Diminished thirst sensation: The body's thirst mechanism can become less sensitive with age, meaning older adults may not feel thirsty even when their body is already dehydrated. This is a primary driver of insufficient fluid intake.
Reduced kidney function: The kidneys of older adults are not as efficient at conserving water. This reduces the body's reserve capacity and ability to respond to fluid loss, increasing the risk of dehydration during illness or in hot weather.
Chronic health conditions: Many conditions common in older adults, such as diabetes and kidney disease, can increase urination and fluid loss. Incontinence can also cause some individuals to intentionally restrict fluid intake to avoid accidents.
Medication side effects: Diuretics, or "water pills," are commonly prescribed for conditions like high blood pressure and heart failure. These medications increase urination and significantly raise the risk of dehydration if fluid intake isn't increased to compensate.
Mobility and cognitive issues: Older adults with reduced mobility may find it difficult to get a drink on their own, while those with cognitive impairments, like dementia, may forget to drink or not recognize their thirst.

Other populations at risk

While infants, children, and older adults are the highest risk groups, other populations are also vulnerable to clinical dehydration under certain circumstances.

Individuals with chronic illnesses: Those with diabetes, kidney disease, cystic fibrosis, and conditions causing persistent vomiting or diarrhea face an elevated risk.
Athletes and outdoor workers: Anyone who engages in vigorous physical activity or works in hot, humid weather sweats heavily, leading to significant fluid loss that must be replaced.
Pregnant women: Dehydration during pregnancy can lead to complications such as preterm labor.

Comparing dehydration risk factors across groups

This table provides a quick overview of how risk factors for dehydration can differ among various populations.


Risk Factor	Infants and Young Children	Older Adults	Athletes/Outdoor Workers
Thirst Sensation	Inability to communicate thirst; less likely to ask for fluids	Diminished or absent thirst sensation	Present, but can lag behind the body's actual needs
Primary Cause	Acute illness (vomiting, diarrhea, fever)	Chronic conditions, medication side effects, lower intake	Excessive sweating from physical exertion
Physiological Makeup	Higher surface-to-mass ratio, greater fluid turnover	Lower total body water percentage, reduced kidney function	Rapid fluid loss through sweat during intense activity
Intervention	Caregiver must actively monitor and provide fluids	Regular reminders, easy access to fluids	Proactive hydration before, during, and after activity

Conclusion: Prevention is key

Clinical dehydration is a serious health concern, and recognizing which group is at the highest risk for clinical dehydration is the first step toward prevention. Infants and older adults are especially vulnerable due to unique physiological and communication challenges. Prevention is the safest and most effective approach for at-risk populations. This involves active monitoring of fluid intake, awareness of symptoms, and addressing underlying health issues. For caregivers, this means being vigilant and proactive, while for active individuals, it means making hydration a routine part of any strenuous activity. For more information on health conditions affecting vulnerable populations, visit the National Institute on Aging website to better understand and manage the unique health challenges associated with aging.

Frequently Asked Questions

Older adults are at a higher risk due to several factors, including a diminished sense of thirst, lower total body fluid volume, decreased kidney function, and the frequent use of medications like diuretics that increase urination. Mobility issues and cognitive decline can also make it difficult for them to access fluids independently.

Infants and children have a higher body surface area to weight ratio and a faster metabolism, which increases fluid loss. They also cannot always communicate that they are thirsty, and common childhood illnesses like diarrhea and vomiting can quickly lead to severe fluid loss.

Signs of dehydration in infants can include decreased urination (fewer wet diapers), a dry mouth and tongue, no tears when crying, sunken eyes or cheeks, and a sunken soft spot (fontanel) on their head. They may also appear listless, cranky, or tired.

The initial signs of dehydration in older adults can be subtle and might include dry mouth, fatigue, headache, or confusion. Since their thirst sensation is often blunted, simply asking if they are thirsty may not be an accurate indicator.

During an illness with vomiting, diarrhea, or fever, caregivers should offer extra fluids frequently. Oral rehydration solutions (ORS), like Pedialyte, are often recommended to replace lost electrolytes. Small, frequent sips are better than large amounts at once to avoid worsening vomiting.

Yes, some medications can increase the risk of dehydration by causing increased urination or sweating. Diuretics (water pills) for high blood pressure are a common example. It is important to discuss medication side effects and proper fluid intake with a healthcare provider.

Other significant risk factors include chronic illnesses such as diabetes and kidney disease, engaging in vigorous exercise, working outdoors in hot weather, and experiencing persistent vomiting or diarrhea from any illness.