Frailty is a common geriatric syndrome. Estimates of frailty's prevalence in older populations may vary according to a number of factors, including the setting in which the prevalence is being estimated – e.g., nursing home (higher prevalence) vs. community (lower prevalence), and the operational definition used for defining frailty. Using the widely used frailty phenotype framework proposed by Fried et al. (2001), prevalence estimates of 7–16% have been reported in non-institutionalized, community-dwelling older adults.

The occurrence of frailty increases incrementally with advancing age, and is more common in older women than men, and among those of lower socio-economic status. Frail older adults are at high risk for major adverse health outcomes, including disability, falls, institutionalization, hospitalization, and mortality.

Epidemiologic research to date has led to the identification of a number of risk factors for frailty, including: (a) chronic diseases, such as cardiovascular disease, diabetes, chronic kidney disease, depression, and cognitive impairment; (b) physiologic impairments, such as activation of inflammation and coagulation systems, anemia, atherosclerosis, autonomic dysfunction, hormonal abnormalities, obesity, hypovitaminosis D in men, and environment-related factors such as life space and neighborhood characteristics. Advances about potentially modifiable risk factors for frailty now offer the basis for translational research effort aimed at prevention and treatment of frailty in older adults. A recent systematic review found that exercise interventions can increase muscle strength and improve physical function; however, results are inconsistent in frail older adults living in the community.

Common causes of heat exhaustion include:

- Hot, sunny, humid weather

- Physical exertion, especially in hot, humid weather

- Due to impaired thermoregulation, elderly people and infants can get serious heat illness even at rest, if the weather outside is hot and humid, and they are not getting enough cool air.

- Some drugs, such as diuretics, antihistamines, beta-blockers, alcohol, ecstasy, and amphetamines can cause an increase in the risk of heat exhaustion.

Especially during physical exertion, risk factors for heat exhaustion include:

- Wearing dark, padded, or insulated clothing; hats; and/or helmets (for example, football pads or turnout gear)

- Having a higher percentage of body fat

- Dehydration

- Fever

- Some medications, like beta blockers and antipsychotic medicines

Osteoporosis is an age-related disease of bone that leads to an increased risk of fracture. In osteoporosis the bone mineral density (BMD) is reduced, bone microarchitecture is disrupted, and the amount and variety of proteins in bone is altered. Osteoporosis is defined by the World Health Organization (WHO) in women as a bone mineral density 2.5 standard deviations below peak bone mass (20-year-old healthy female average) as measured by DXA; the term "established osteoporosis" includes the presence of a fragility fracture.

Osteoporosis is most common in women after menopause, when it is called "postmenopausal osteoporosis", but may also develop in men, and may occur in anyone in the presence of particular hormonal disorders and other chronic diseases or as a result of medications, specifically glucocorticoids, when the disease is called steroid- or glucocorticoid-induced osteoporosis (SIOP or GIOP). Given its influence in the risk of fragility fracture, osteoporosis may significantly affect life expectancy and quality of life.

First aid for heat exhaustion includes:

- Moving the person to a cool place

- Having the patient take off extra layers of clothes

- Cooling the patient down by fanning them and putting wet towels on their body

- Having them lie down and put their feet up if they are feeling dizzy

- Having them drink water or sports drinks – but only if they are awake, not confused nor vomiting

- Turning the person on their side if they are vomiting

The six-week period after pregnancy is called the postpartum stage. During this time, women are at increased risk of being constipated. Multiple studies estimate the prevalence of constipation to be around 25% during the first 3 months. Constipation can cause discomfort for women, as they are still recovering from the delivery process especially if they have had a perineal tear or underwent an episiotomy. Risk factors that increase the risk of constipation in this population include:

- Damage to the levator ani muscles (pelvic floor muscles) during childbirth

- Forceps-assisted delivery

- Lengthy second stage of labor

- Delivering a large child

- Hemorrhoids

Hemorrhoids are common in pregnancy and also may get exacerbated when constipated. Anything that can cause pain with stooling (hemorrhoids, perineal tear, episiotomy) can lead to constipation because patients may withhold from having a bowel movement so as to avoid pain.

The pelvic floor muscles play an important role in helping pass a bowel movement. Injury to those muscles by some of the above risk factors (examples- delivering a large child, lengthy second stage of labor, forceps delivery) can result in constipation. Women sometimes get enemas during labor that can also alter bowel movements in the days after having given birth. However, there is insufficient evidence to make conclusions about the effectiveness and safety of laxatives in this group of people.

Infants who are colicky do just as well as their non colicky peers with respect to temperament at one year of age.

Heat cramps, a type of heat illness, are muscle spasms that result from loss of large amount of salt and water through exercise. Heat cramps are associated with cramping in the abdomen, arms and calves. This can be caused by inadequate consumption of fluids or electrolytes. Frequently, they don't occur until sometime later, especially at night or when relaxing. Heavy sweating causes heat cramps, especially when the water is replaced without also replacing salt or potassium.

Although heat cramps can be quite painful, they usually don't result in permanent damage, though they can be a symptom of heat stroke or heat exhaustion. Heat cramps can indicate a more severe problem in someone with heart disease or if they last for longer than an hour.

In order to prevent them, one may drink electrolyte solutions such as sports drinks during exercise or strenuous work or eat potassium-rich foods like bananas and apples. When heat cramps occur, the affected person should avoid strenuous work and exercise for several hours to allow for recovery.

Chronic fatigue syndrome is a name for a group of diseases that are dominated by persistent fatigue. The fatigue is not due to exercise and is not relieved by rest.

Through numerous studies, it has been shown that people with chronic fatigue syndrome have an integral central fatigue component. In one study, the subjects' skeletal muscles were checked to ensure they had no defects that prevented their total use. It was found that the muscles functioned normally on a local level, but they failed to function to their full extent as a whole. The subjects were unable to consistently activate their muscles during sustained use, despite having normal muscle tissue. In another study, the subjects experienced higher perceived effort in relation to heart rate as compared to the control during a graded exercise test. The chronic fatigue subjects would stop before any sort of limit on the body was reached. Both studies proved that peripheral muscle fatigue was not causing the subjects with chronic fatigue syndrome to cease exercising. It is possible that the higher perception of effort required to use the muscles results in great difficulty in accomplishing consistent exercise. The main cause of fatigue in chronic fatigue syndrome most likely lies in the central nervous system. A defect in one of its components could cause a greater requirement of input to result in sustained force. It has been shown that with very high motivation, subjects with chronic fatigue can exert force effectively. Further investigation into central nervous system fatigue may result in medical applications.

Central nervous system fatigue, or central fatigue, is a form of fatigue that is associated with changes in the synaptic concentration of neurotransmitters within the central nervous system (CNS; including the brain and spinal cord) which affects exercise performance and muscle function and cannot be explained by peripheral factors that affect muscle function. In healthy individuals, central fatigue can occur from prolonged exercise and is associated with neurochemical changes in the brain, primarily involving serotonin (5-HT), noradrenaline, and dopamine. Central fatigue plays an important role in endurance sports and also highlights the importance of proper nutrition in endurance athletes.

Causes of such breakdowns are varied. A 1996 study found that problems with intimate relationships, such as divorce or marital separation, contributed to 24% of nervous breakdowns. Problems at work and school accounted for 17% of cases, and financial problems for 11%. Surveys suggest that in the United States, health problems have decreased in importance as a contributor to nervous breakdowns. Health problems accounted for 28% of nervous breakdowns in 1957, 12% in 1976, and only 5.6% in 1996.

A nervous breakdown is very similar to a panic attack. Stress is a major cause in both cases and they are both temporary. During a nervous breakdown, a person's emotional state of being shifts from an ability to cope with life stresses to a state of being totally overwhelmed to a point that normal functioning is disrupted. Excessive worry, nervousness, fear, anxiety are symptomatic. These states of being are accompanied by a variety of uncomfortable feelings often summarized as bad or sad. If these feelings become so intense they are perceived as life-threatening, the defense system blocks awareness. These mechanisms while protective can also be limiting to successful living. Overwhelming stress, therefore, is causative. Whether that stress is self-created or external requires different approaches and has different implications to the individual.

A nervous breakdown is not limited to any one type of person: anyone can have this breakdown, but if someone is under a lot of stress and has a family background of mental disorders, they can be more likely to have one.

Rapport, Todd, Lumley, and Fisicaro suggest that the closest DSM-IV diagnostic category to nervous breakdown is Adjustment Disorder with Mixed Anxiety and Depressed Mood (Acute). Adjustment disorders and nervous breakdowns are both acute reactions to stress that resolve after removal of the stressor. However, DSM-IV excludes from adjustment disorders cases secondary to bereavement, which contributes to approximately 6–8% of nervous breakdowns.

Nervous breakdowns may share some features of acute stress disorder and post-traumatic stress disorder, in that these each occur in response to an external stressor, and may be marked with sleep disturbance, diminished concentration, and mood lability. However, the symptoms of nervous breakdown do not include the constellation of re-experienced trauma, dissociation, avoidance, and numbing of general responsiveness that are associated with the other two disorders, and the types of stressors linked to a nervous breakdown are generally less extreme.

Nervous breakdowns may share many features of mixed anxiety-depressive disorder (MADD). However, the definition of MADD suggests a chronic condition, in contrast to the acute, short-term nature of a nervous breakdown.

Faintness, dizziness, headache, increased pulse, restlessness, nausea, vomiting, and brief loss of consciousness.

Approximately 3% of children have constipation, with girls and boys being equally affected. With constipation accounting for approximately 5% of general pediatrician visits and 25% of pediatric gastroenterologist visits, the symptom carries a significant financial impact upon the healthcare system. While it is difficult to assess an exact age at which constipation most commonly arises, children frequently suffer from constipation in conjunction with life-changes. Examples include: toilet training, starting or transferring to a new school, and changes in diet. Especially in infants, changes in formula or transitioning from breast milk to formula can cause constipation. Fortunately, the majority of constipation cases are not tied to a medical disease, and treatment can be focused on simply relieving the symptoms.

Heat syncope occurs in a warm environment when blood pressure is lowered as the body dilates (widens) arterioles (small blood vessels) in the skin to radiate heat. This condition occurs within five days of heat acclimatization, before the blood volume expands. The result is less blood to the brain, causing light-headedness and fainting when a person stands up quickly or stands for a long period of time. Those who perform strenuous work outside in warm climates are at particular risk.

For the individual, prevention consists of ensuring they eat plenty of food, varied enough to provide a nutritionally complete diet.

Starvation can be caused by factors, other than illness, outside of the control of the individual. The Rome Declaration on World Food Security outlines several policies aimed at increasing food security and, consequently, preventing starvation. These include:

- Poverty reduction

- Prevention of wars and political instability

- Food aid

- Agricultural sustainability

- Reduction of economic inequality

Supporting farmers in areas of food insecurity through such measures as free or subsidized fertilizers and seeds increases food harvest and reduces food prices.

Starvation is a severe deficiency in caloric energy intake, below the level needed to maintain an organism's life. It is the most extreme form of malnutrition. In humans, prolonged starvation can cause permanent organ damage and eventually, death. The term inanition refers to the symptoms and effects of starvation. Starvation may also be used as a means of torture or execution.

According to the World Health Organization, hunger is the single gravest threat to the world's public health. The WHO also states that malnutrition is by far the biggest contributor to child mortality, present in half of all cases. Undernutrition is a contributory factor in the death of 3.1 million children under five every year. Figures on actual starvation are difficult to come by, but according to the Food and Agriculture Organization, the less severe condition of undernourishment currently affects about 842 million people, or about one in eight (12.5%) people in the world population.

The bloated stomach, as seen in the adjacent picture, represents a form of malnutrition called kwashiorkor which is caused by insufficient protein despite a sufficient caloric intake. Better medicine will prevent the pictured symptoms in which included is weight loss and muscle wasting from further taking form.

According to one hypothesis, "POIS is caused by Type-I and Type-IV allergy to the males' own semen". Specifically,

POIS could also be caused by an auto-immune reaction not to semen itself, but to another substance that is released during ejaculation, such as to cytokines.

The allergy hypothesis has been disputed. According to one study, "IgE-mediated semen allergy in men may not be the potential mechanism of POIS".

The cause of POIS is unknown. Some doctors hypothesize that POIS is caused by an auto-immune reaction. Other doctors suspect a hormone imbalance as the cause. While other causes have been proposed as well, none of the proposed causes seem to fully explain the disease.

Prevention includes avoiding medications that can increase the risk of heat illness (e.g. antihypertensives, diuretics, and anticholinergics), gradual adjustment to heat, and sufficient fluids and electrolytes.

Heat stroke is relatively common in sports and is the cause of about 2 percent of deaths. Football in the United States has the highest rates.

Between 1999 and 2003, the US had a total of 3442 deaths from heat illness. Those who work outdoors are at particular risk for heat illness, though those who work in poorly-cooled spaces indoors are also at risk. Between 1992 and 2006, 423 workers died from heat illness in the US.

Besides complications of surgery and anesthesia in general, there may be drainage, swelling, or redness of the incision, gagging or coughing during eating or drinking, or pneumonia due to aspiration of food or liquids. Undesirable complications are estimated to occur in 10-30% of cases. If medical therapy is unsuccessful and surgery cannot be performed due to concurrent disease (such as heart or lung problems) or cost, euthanasia may be necessary if the animal's quality of life is considered unacceptable due to the disease.

Those working in industry, in the military, or as first responders may be required to wear personal protective equipment (PPE) against hazards such as chemical agents, gases, fire, small arms and even Improvised Explosive Devices (IEDs). PPE includes a range of hazmat suits, firefighting turnout gear, body armor and bomb suits, among others. Depending on design, the wearer may be encapsulated in a microclimate, due to an increase in thermal resistance and decrease in vapor permeability. As physical work is performed, the body’s natural thermoregulation (i.e., sweating) becomes ineffective. This is compounded by increased work rates, high ambient temperature and humidity levels, and direct exposure to the sun. The net effect is that desired protection from some environmental threats inadvertently increases the threat of heat stress.

The effect of PPE on hyperthermia has been noted in fighting the 2014 Ebola virus epidemic in Western Africa. Doctors and healthcare workers were only able to work 40 minutes at a stretch in their protective suits, fearing heat strokes.

Situational heat stroke occurs in the absence of exertion. It mostly affects the young and elderly. In the elderly in particular, it can be precipitated by medications that reduce vasodilation and sweating, such as anticholinergic drugs, antihistamines, and diuretics. In this situation, the body's tolerance for high environmental temperature may be insufficient, even at rest.

Heat waves are often followed by a rise in the death rate, and these 'classical hyperthermia' deaths typically involve the elderly and infirm. This is partly because thermoregulation involves cardiovascular, respiratory and renal systems which may be inadequate for the additional stress because of the existing burden of aging and disease, further compromised by medications. During the July 1995 heat wave in Chicago, there were at least 700 heat-related deaths. The strongest risk factors were being confined to bed, and living alone, while the risk was reduced for those with working air conditioners and those with access to transportation. Even then, reported deaths may be underestimates as diagnosis can be misclassified as stroke or heart attack.

There is an increased risk that statin (cholesterol-reducing drugs) will cause myopathy (muscle weakness) in individuals with MADD.

Anesthesia has the potential to cause malignant hyperthermia, an uncontrolled increase in body temperature, and permanent muscle damage in patients with MADD. Individuals with MADD are advised to notify their anesthesiologist about their condition prior to surgery.

In most cases where myopathy is present with MADD, a second muscle disease is present and symptoms are worse than either disease in isolation.

Colic affects 10–40% of children. occurring at the same rate in boys and in girls.