Abigail Loraine "Abby" Hensel and Brittany Lee Hensel (born March 7, 1990) are American dicephalic parapagus twins; in other words, they are conjoined twins, each of whom has a separate head, but whose bodies are joined.

They are highly symmetric for conjoined twins, giving the appearance of having a single body without marked variation from normal proportions. In fact, several vital organs are doubled; each twin has a separate heart, stomach, spine, pair of lungs, and spinal cord.

Each twin controls her half of their body, operating one arm and one leg. As infants, the initial learning of physical processes that required bodily coordination, such as clapping, crawling, and walking, required the cooperation of both twins.

While they can eat and write separately and simultaneously, activities such as running and swimming require them to coordinate and alternate their actions symmetrically. Other activities as diverse as brushing hair and driving a car require each twin to perform separate actions that coordinate with the other's.

Due to the curiosity that their condition generated, the twins' progress as they were growing up was covered in a number of popular media, including "Life" magazine and "The Oprah Winfrey Show". At the age of 16, they gave an interview on The Learning Channel on December 17, 2006, in which they discussed aspects of their daily lives and plans for the future. They starred in their own reality series, "Abby & Brittany", on TLC in 2012.

The twins have a single body with separate heads and necks, a chest that is wider than normal, two arms, and two legs. At birth, they had a rudimentary arm between the bases of their necks attached to a shoulder blade at the back, being combined parts of Abby's left arm and Brittany's right arm. It was removed, leaving the shoulder blade.

Abby's head tilts laterally outward about 5 degrees to the right, while Brittany's tilts laterally at about 15 degrees to the left, causing her to appear shorter even when seated. Brittany's leg is in fact nearly two inches shorter than Abby's and Brittany tends to stand and walk on tip-toe which has made her calf muscle significantly larger than Abby's. The continued growth of Abby's spine was surgically halted after Brittany prematurely stopped growing. At age 12, they underwent surgery at Gillette Children's Specialty Healthcare to correct scoliosis and to expand their chest cavity to prevent future difficulties with breathing.

Each twin manages one side of their conjoined body. The sense of touch of each is restricted to her body half; this shades off at the midsagittal plane such that there is a small amount of overlap at the midline. Stomach aches, however, are felt only by the twin on the opposite side.

They are effective in cooperatively using their limbs when both hands or both legs are required. By coordinating their efforts, they are able to walk, run, swim, and ride a bicycle normally—all tasks that they learned at a normal speed. Together, they can type on a computer keyboard at a normal speed and drive a car. However, their disparate heights (Abby, , is taller and longer of leg than Brittany, ) led to difficulty in balancing a Segway, as shown in their 2012 reality series.

Polycephaly is the condition of having more than one head. The term is derived from the Egyptian stems "poly" (Greek: "πολύ") meaning "many" and "kephalē" (Greek: "κεφάλη") meaning "head". A polycephalic organism may be thought of as one being with a supernumerary body part, or as two or more beings with a shared body.

Two-headed animals (called bicephalic or dicephalic) and three-headed (tricephalic) animals are the only type of multi-headed creatures seen in the real world, and form by the same process as conjoined twins from monozygotic twin embryos.

In humans, there are two forms of twinning that can lead to two heads being supported by a single torso. In dicephalus parapagus dipus, the two heads are side by side. In craniopagus parasiticus, the two heads are joined directly to each other, but only one head has a functional torso. Survival to adulthood is rare, but does occur in some forms of dicephalus parapagus dipus.

There are many occurrences of multi-headed animals in mythology. In heraldry and vexillology, the double-headed eagle is a common symbol, though no such animal is known to have ever existed.

Two-headed people and animals, though rare, have long been known to exist and documented.

"'Conjoined twins" are identical twins joined in utero. An extremely rare phenomenon, the occurrence is estimated to range from 1 in 49,000 births to 1 in 189,000 births, with a somewhat higher incidence in Southeast Asia and Africa. Approximately half are stillborn, and an additional one-third die within 24 hours. Most live births are female, with a ratio of 3:1.

Two contradicting theories exist to explain the origins of conjoined twins. The more generally accepted theory is "fission", in which the fertilized egg splits partially. The other theory, no longer believed to be the basis of conjoined twinning, is fusion, in which a fertilized egg completely separates, but stem cells (which search for similar cells) find like-stem cells on the other twin and fuse the twins together. Conjoined twins share a single common chorion, placenta, and amniotic sac, although these characteristics are not exclusive to conjoined twins as there are some monozygotic but non-conjoined twins who also share these structures in utero.

The most famous pair of conjoined twins was Chang and Eng Bunker (Thai: อิน-จัน, In-Chan) (1811–1874), Thai brothers born in Siam, now Thailand. They traveled with P.T. Barnum's circus for many years and were labeled as the Siamese twins. Chang and Eng were joined at the torso by a band of flesh, cartilage, and their fused livers. In modern times, they could have been easily separated. Due to the brothers' fame and the rarity of the condition, the term "Siamese twins" came to be used as a synonym for conjoined twins.

One reason that poverty produces such high rates of fistula cases is the malnutrition that exists in such areas. Lack of money and access to proper nutrition, as well as vulnerability to diseases that exist in impoverished areas because of limited basic health care and disease prevention methods, cause inhabitants of these regions to experience stunted growth. Sub-Saharan Africa is one such environment where the shortest women have on average lighter babies and more difficulties during birth when compared with full-grown women. This stunted growth causes expectant mothers to have skeletons unequipped for proper birth, such as an underdeveloped pelvis. This weak and underdeveloped bone structure increases the chances that the baby will get stuck in the pelvis during birth, cutting off circulation and leading to tissue necrosis. Because of the correlation between malnutrition, stunted growth, and birthing difficulties, maternal height can at times be used as a measure for expected labor difficulties.

High levels of poverty also lead to low levels of education among impoverished women concerning maternal health. This lack of information in combination with obstacles preventing rural women to easily travel to and from hospitals lead many to arrive at the birthing process without prenatal care. This can cause a development of unplanned complications that may arise during home births, in which traditional techniques are used. These techniques often fail in the event of unplanned emergencies, leading women to go to hospital for care too late, desperately ill, and therefore vulnerable to the risks of anesthesia and surgery that must be used on them. In a study of women who had prenatal care and those who had unbooked emergency births, “the death rate in the booked-healthy group was as good as that in many developed countries, [but] the death rate in the unbooked emergencies was the same as the death rate in England in the 16th and 17th centuries.” In this study, 62 unbooked emergency women were diagnosed with obstetric fistulae out of 7,707 studied, in comparison to three diagnosed booked mothers out of 15,020 studied. In addition, studies find that education is associated with lower desired family size, greater use of contraceptives, and increased use of professional medical services. Educated families are also more likely to be able to afford health care, especially maternal healthcare.

Embryo splitting in which zygote divide asexually,

to produce identical children, is blocked by mitosis inhibitor.

In Chinese alchemy, elixir poisoning refers to the toxic effects from elixirs of immortality that contained metals and minerals such as mercury and arsenic. The official "Twenty-Four Histories" record numerous Chinese emperors, nobles, and officials who ironically died from taking elixirs in order to prolong their lifespans. The first emperor to die from elixir poisoning was likely Qin Shi Huang (d. 210 BCE) and the last was Yongzheng (d. 1735). Despite common knowledge that immortality potions could be deadly, fangshi and Daoist alchemists continued the elixir-making practice for two millennia.

The causes of childhood obesity can be based on both a combination of individual choices and socio-environmental adaptions with genetic factors playing an important role also.

The association with Anne of Denmark is based on portraiture, although history does not suggest that she suffered an underactive thyroid. The eponym is disputed by some, though it has been suggested that Anne of France, Anne of Brittany, Anne of Austria, Anne Boleyn and Anne of Cleves may all be eliminated as candidates.

The medical condition of being overweight or obesity is defined as "abnormal or excessive fat accumulation that may impair health". It is measured through the Body Mass Index (BMI), defined as a person's weight, in kilograms, divided by the square of the person's height, in meters. If an individual has a BMI of 25–29, he or she is overweight. Having a BMI of 30 or more means an individual is obese. The greater the BMI, the greater the risk of chronic diseases as a result of obesity. These diseases include cardiovascular diseases, diabetes, musculoskeletal disorders, cancer, and premature death.

Genetics, according to the Australian Health Survey plays a primary role in determining obesity. In 2011/2012 it was recorded that 90% of the Australian population had inherited their obese tendencies due to the epigenetic modifications of their mothers during pregnancy. Interchanging closely with the genetic factor, the environment and individual temptations are also highlighted as contributing causes to the worldwide epidemic. The genetic configuration influences the tendencies to become overweight, and diet and physical activity determines to what extent those tendencies are elaborated.

Being an extremely rare disease, it is unknown as to what exactly causes Panner Disease. It is believed that the disease may be brought on by continuous overuse of the elbow and that puts pressure on the elbow and also strains the elbow in children during the period of rapid bone growth. The overuse of the elbow can be due to the involvement in sports such as baseball, handball, and gymnastics where these sports involve throwing or putting a lot of pressure on the joints. These repeated activities cause microtraumas and results in the affected elbow being swollen, irritated, and in pain. Panner Disease results when the blood supply to the capitellum is disrupted and therefore the cells within the growth plate of the capitellum die and it becomes flat due to the softening and collapsing of the surrounding bone. To prevent future instances of Panner Disease the child is instructed to cease all physical and sports activities that involve the use of the affected elbow until the symptoms are relieved.

The Sign of Hertoghe or Queen Anne's sign is a thinning or loss of the outer third of the eyebrows, and is a classical sign of hypothyroidism or dermatitis atopica, but it can also be detected in lepromatous leprosy. The sign is named after Eugene Hertoghe of Antwerp, a pioneer in thyroid function research.

The MONICA Project, sponsored by the World Health Organization, discovered that 30% of the population in the Arab World is overweight or obese, including adolescents and adults. This percentage is smaller for North African countries than oil-producing countries, but is still a prevalent trend. The spread of the Western lifestyle, defined as "the intake of attractive energy dense food with undesirable composition, increased consumption of animal fats and sugars and reduced consumption of dietary fiber, along with a lack of sufficient physical activity", is one of the leading causes. Specifically in the Arabian Peninsula, "physical activity of the population has significantly diminished with the availability of housemaids, private cars, television, and sophisticated household appliances. In addition, the types of food and fat intake have changed...".

Other common factors, besides a sedentary lifestyle and unhealthy food choices, across the Arab world include urbanization, technology, and a cultural appreciation of female plumpness and the practice of "leblouh" ("fattening").

Heat-related illnesses from occupational heat stress have several risk factors. Some of these factors include high temperatures, humidity, radiant heat sources, limited air movement, metabolic heat from physical exertion of energy, not drinking enough fluids, personal protective equipment and clothing, physical condition and health problems, medications, pregnancy, lack of acclimatization, advanced age, having a previous heat-related illness and others.

Occupational heat stress is the net load to which a worker is exposed from the combined contributions of metabolic heat, environmental factors, and clothing worn which results in an increase in heat storage in the body. Heat stress can result in heat-related illnesses, such as heat stroke, hyperthermia, heat exhaustion, heat cramps or heat rashes. Although heat exhaustion is less severe, hyperthermia is a medical emergency and requires emergency treatment, which if not provided can even lead to death.

Heat stress causes illness but also may account for an increase in workplace accidents, and a decrease in worker productivity. Worker injuries attributable to heat include those caused by: sweaty palms, fogged-up safety glasses, and dizziness. Burns may also occur as a result of accidental contact with hot surfaces or steam. In United States, occupational heat stress in becoming more significant as the average temperatures increase but remains overlooked. There are few studies and regulations regarding heat exposure of workers.

There is most likely a link between children's linear growth and household sanitation practices. The ingestion of high quantities of fecal bacteria by young children through putting soiled fingers or household items in the mouth leads to intestinal infections. This affect children's nutritional status by diminishing appetite, reducing nutrient absorption, and increasing nutrient losses.

The diseases recurrent diarrhoea and intestinal worm infections (helminthiasis) which are both linked to poor sanitation have been shown to contribute to child stunting. The evidence that a condition called environmental enteropathy also stunts children is not conclusively available yet, although the link is plausible and several studies are underway on this topic. Environmental enteropathy is a syndrome causing changes in the small intestine of persons and can be brought on due to lacking basic sanitary facilities and being exposed to faecal contamination on a long-term basis.

Research on a global level has found that the proportion of stunting that could be attributed to five or more episodes of diarrhoea before two years of age was 25%. Since diarrhoea is closely linked with water, sanitation and hygiene (WASH), this is a good indicator for the connection between WASH and stunted growth. To what extent improvements in drinking water safety, toilet use and good handwashing practices contribute to reduce stunting depends on the how bad these practices were prior to interventions.

Poor maternal nutrition during pregnancy and breastfeeding can lead to stunted growth of their children. Women who are underweight or anemic during pregnancy, are more likely to have stunted children which perpetuates the inter-generational transmission of stunting.

Although the exact cause of Panner Disease is unknown, in recent research, it has been concluded that it may be associated with frequent throwing or other athletic activity. In the same article that talks about varying osteochondrosis diseases, it is pointed out that Panner Disease always involves alteration of the capitellum, which can be visualized by radiography. In another research article, the research team aimed to summarize the best available evidence for diagnosis and treatment for Panner Disease. In the article it was found that the most common symptoms that patients with Panner Disease present with are elbow stiffness and swelling, limited range of motion, and limited elbow extension. In alignment with the previously mentioned article, the team of researchers also concluded that Panner Disease involves irregularity of the capitellum, specifically that it appears flattened. Panner Disease often gets misdiagnosed as osteochondritis dissecans (OCD), and in this article they distinguish the difference between the two diseases are age difference and radiographic findings. In alignment with the two previously discussed articles, another article that reports on three case studies of Panner Disease, states that the primary treatment that is used for Panner Disease is rest and restriction from all physical and athletic activity that involves the use of the upper extremities; the activity is suggested to be ceased until the symptoms are relieved.

Though heart disease is not exclusive to the poor, there are aspects of a life of poverty that contribute to its development. This category includes coronary heart disease, stroke and heart attack. Heart disease is the leading cause of death worldwide and there are disparities of morbidity between the rich and poor. Studies from around the world link heart disease to poverty. Low neighborhood income and education were associated with higher risk factors. Poor diet, lack of exercise and limited (or no) access to a specialist were all factors related to poverty, though to contribute to heart disease.

Both low income and low education were predictors of coronary heart disease, a subset of cardiovascular disease. Of those admitted to hospital in the United States for heart failure, women and African Americans were more likely to reside in lower income neighborhoods. In the developing world, there is a 10 fold increase in cardiac events in the black and urban populations.

Although the incidence of underage drinking is still significant, government, university and national statistics have confirmed that alcohol use and binge drinking among high school students has declined steadily over the past three decades, and continues to decline annually. According to a United States Substance Abuse and Mental Health Services Administration study involving 30,000 youths aged 12 to 20 years old, between 2002 and 2013 the percentage of underage drinkers declined from 28.8% to 22.7%. Underage binge drinkers decreased 19.3% to 14.2%. A December 2014 study performed by the University of Michigan also found that 75% of senior high school students disapproved of drinking excessively on the weekends. Alcohol still proved to be the favored substance of abuse among American youths however, with tobacco and illicit drugs following in rank.

The proximal causes of fiddler’s neck are friction and pressure, but both repetitive shearing stress and occlusion with consequent trapping of sweat give rise to progressive damage. This damage along with poor hygiene predisposes the area to local infection, and such infection can progress to scarring and other long-term effects. Hot weather is reported to exacerbate fiddler’s neck, as are tiredness, playing emotional music, and playing in smaller groups where individual stress is higher. Type I hypersensitivity reactions may also be involved, particularly to rosewood and ebony in the chinrest and tailpiece, as well as to varnish of the instrument body when chinrests are not used and to rosin deposits on the instrument and on chin cloths. Nickel or other metal allergies are common causes if the chin rest has a metal clip that comes into constant contact with the skin. Rosin exposure in particular may lead to abietic acid dermatitis.

A survey of over 6000 teenagers revealed (1):

- Teenagers and young adults typically get their alcohol from persons 21 or older. The second most common source for high school students is someone else under age 21, and the third most common source for 18- to 20-year-old adults is buying it from a store, bar or restaurant (despite the fact that such sales are against the law).

- In the 12th grade, boys were more likely than girls to buy alcohol from a store, bar or restaurant.

- The higher a teenager's weekly income, the more likely he/she will buy alcohol from a store, bar or restaurant.

- It is easy to get alcohol at a party and from siblings or others 21 or older.

How easy is it for youth to buy alcohol?

- When young females attempted to buy beer without an ID at liquor, grocery or convenience stores, 47–52% of the attempts, beer was sold (1, 2) and nearly 80% of all the stores sold beer to the buyers at least once in three attempts; nearly 25% sold beer all three times.(1)

- When young females attempted to buy beer without an ID at bars or restaurants, 50% of the attempts resulted in a sale to the buyer.(2)

- When young males and females attempted to buy beer without an ID at community festivals, 50% of the attempts resulted in a sale to the buyer.(3)