A number of factors make people more susceptible to TB infections. The most important risk factor globally is HIV; 13% of all people with TB are infected by the virus. This is a particular problem in sub-Saharan Africa, where rates of HIV are high. Of people without HIV who are infected with tuberculosis, about 5–10% develop active disease during their lifetimes; in contrast, 30% of those coinfected with HIV develop the active disease.

Tuberculosis is closely linked to both overcrowding and malnutrition, making it one of the principal diseases of poverty. Those at high risk thus include: people who inject illicit drugs, inhabitants and employees of locales where vulnerable people gather (e.g. prisons and homeless shelters), medically underprivileged and resource-poor communities, high-risk ethnic minorities, children in close contact with high-risk category patients, and health-care providers serving these patients.

Chronic lung disease is another significant risk factor. Silicosis increases the risk about 30-fold. Those who smoke cigarettes have nearly twice the risk of TB compared to nonsmokers.

Other disease states can also increase the risk of developing tuberculosis. These include alcoholism and diabetes mellitus (three-fold increase).

Certain medications, such as corticosteroids and infliximab (an anti-αTNF monoclonal antibody), are becoming increasingly important risk factors, especially in the developed world.

Genetic susceptibility also exists, for which the overall importance remains undefined.

A person's sex also seems to have some role in the development of autoimmunity; that is, most autoimmune diseases are "sex-related". Nearly 75% of the more than 23.5 million Americans who suffer from autoimmune disease are women, although it is less-frequently acknowledged that millions of men also suffer from these diseases. According to the American Autoimmune Related Diseases Association (AARDA), autoimmune diseases that develop in men tend to be more severe. A few autoimmune diseases that men are just as or more likely to develop as women include: ankylosing spondylitis, type 1 diabetes mellitus, granulomatosis with polyangiitis, Crohn's disease, Primary sclerosing cholangitis and psoriasis.

The reasons for the sex role in autoimmunity vary. Women appear to generally mount larger inflammatory responses than men when their immune systems are triggered, increasing the risk of autoimmunity. Involvement of sex steroids is indicated by that many autoimmune diseases tend to fluctuate in accordance with hormonal changes, for example: during pregnancy, in the menstrual cycle, or when using oral contraception. A history of pregnancy also appears to leave a persistent increased risk for autoimmune disease. It has been suggested that the slight, direct exchange of cells between mothers and their children during pregnancy may induce autoimmunity. This would tip the gender balance in the direction of the female.

Another theory suggests the female high tendency to get autoimmunity is due to an imbalanced X chromosome inactivation. The X-inactivation skew theory, proposed by Princeton University's Jeff Stewart, has recently been confirmed experimentally in scleroderma and autoimmune thyroiditis. Other complex X-linked genetic susceptibility mechanisms are proposed and under investigation.

A more common cause is excessive loss of potassium, often associated with heavy fluid losses that "flush" potassium out of the body. Typically, this is a consequence of diarrhea, excessive perspiration, or losses associated with muscle-crush injury, or surgical procedures. Vomiting can also cause hypokalemia, although not much potassium is lost from the vomitus. Rather, heavy urinary losses of K in the setting of postemetic bicarbonaturia force urinary potassium excretion (see Alkalosis below). Other GI causes include pancreatic fistulae and the presence of adenoma.

Perhaps the most obvious cause is insufficient consumption of potassium (that is, a low-potassium diet) or starvation. However, without excessive potassium loss from the body, this is a rare cause of hypokalemia.

Usually only seen in anorexia nervosa patients and people on a ketogenic diet.

Progression from TB infection to overt TB disease occurs when the bacilli overcome the immune system defenses and begin to multiply. In primary TB disease (some 1–5% of cases), this occurs soon after the initial infection. However, in the majority of cases, a latent infection occurs with no obvious symptoms. These dormant bacilli produce active tuberculosis in 5–10% of these latent cases, often many years after infection.

The risk of reactivation increases with immunosuppression, such as that caused by infection with HIV. In people coinfected with "M. tuberculosis" and HIV, the risk of reactivation increases to 10% per year. Studies using DNA fingerprinting of "M. tuberculosis" strains have shown reinfection contributes more substantially to recurrent TB than previously thought, with estimates that it might account for more than 50% of reactivated cases in areas where TB is common. The chance of death from a case of tuberculosis is about 4% as of 2008, down from 8% in 1995.

An interesting inverse relationship exists between infectious diseases and autoimmune diseases. In areas where multiple infectious diseases are endemic, autoimmune diseases are quite rarely seen. The reverse, to some extent, seems to hold true. The hygiene hypothesis attributes these correlations to the immune manipulating strategies of pathogens. While such an observation has been variously termed as spurious and ineffective, according to some studies, parasite infection is associated with reduced activity of autoimmune disease.

The putative mechanism is that the parasite attenuates the host immune response in order to protect itself. This may provide a serendipitous benefit to a host that also suffers from autoimmune disease. The details of parasite immune modulation are not yet known, but may include secretion of anti-inflammatory agents or interference with the host immune signaling.

A paradoxical observation has been the strong association of certain microbial organisms with autoimmune diseases.

For example, "Klebsiella pneumoniae" and coxsackievirus B have been strongly correlated with ankylosing spondylitis and diabetes mellitus type 1, respectively. This has been explained by the tendency of the infecting organism to produce super-antigens that are capable of polyclonal activation of B-lymphocytes, and production of large amounts of antibodies of varying specificities, some of which may be self-reactive (see below).

Certain chemical agents and drugs can also be associated with the genesis of autoimmune conditions, or conditions that simulate autoimmune diseases. The most striking of these is the drug-induced lupus erythematosus. Usually, withdrawal of the offending drug cures the symptoms in a patient.

Cigarette smoking is now established as a major risk factor for both incidence and severity of rheumatoid arthritis. This may relate to abnormal citrullination of proteins, since the effects of smoking correlate with the presence of antibodies to citrullinated peptides.

The causes of PTSD are: Natural or human disasters, war, serious accident, witness of violent death of others, violent attack, being the victim of sexual abuse, rape, torture, terrorism or hostage taking.

Predisposing factors

The predisposing factors are: Personality traits and Previous history of Psychiatric illness.

Psychiatric consultation: Exploration of memories of the traumatic event, relief of associated symptoms and counseling.

Anisocoria is a common condition, defined by a difference of 0.4 mm or more between the sizes of the pupils of the eyes.

Anisocoria has various causes:

- Physiological anisocoria: About 20% of normal people have a slight difference in pupil size which is known as physiological anisocoria. In this condition, the difference between pupils is usually less than 1 mm.

- Horner's syndrome

- Mechanical anisocoria: Occasionally previous trauma, eye surgery, or inflammation (uveitis, angle closure glaucoma) can lead to adhesions between the iris and the lens.

- Adie tonic pupil: Tonic pupil is usually an isolated benign entity, presenting in young women. It may be associated with loss of deep tendon reflex (Adie's syndrome). Tonic pupil is characterized by delayed dilation of iris especially after near stimulus, segmental iris constriction, and sensitivity of pupil to a weak solution of pilocarpine.

- Oculomotor nerve palsy: Ischemia, intracranial aneurysm, demyelinating diseases (e.g., multiple sclerosis), head trauma, and brain tumors are the most common causes of oculomotor nerve palsy in adults. In ischemic lesions of the oculomotor nerve, pupillary function is usually spared whereas in compressive lesions the pupil is involved.

- Pharmacological agents with anticholinergic or sympathomimetic properties will cause anisocoria, particularly if instilled in one eye. Some examples of pharmacological agents which may affect the pupils include pilocarpine, cocaine, tropicamide, MDMA, dextromethorphan, and ergolines. Alkaloids present in plants of the genera "Brugmansia" and "Datura", such as scopolamine, may also induce anisocoria.

- Migraines

Anisocoria is a condition characterized by an unequal size of the eyes' pupils. Affecting 20% of the population, it can be an entirely harmless condition or a symptom of more serious medical problems.

Because there is uncertainty in treating suspected factitious disorder imposed on self, some advocate that health care providers first explicitly rule out the possibility that the person has another early-stage disease. Then they may take a careful history and seek medical records to look for early deprivation, childhood abuse, or mental illness. If a person is at risk to themself, psychiatric hospitalization may be initiated.

Healthcare providers may consider working with mental health specialists to help treat the underlying mood or disorder as well as to avoid countertransference. Therapeutic and medical treatment may center on the underlying psychiatric disorder: a mood disorder, an anxiety disorder, or borderline personality disorder. The patient's prognosis depends upon the category under which the underlying disorder falls; depression and anxiety, for example, generally respond well to medication and/or cognitive behavioral therapy, whereas borderline personality disorder, like all personality disorders, is presumed to be pervasive and more stable over time, and thus offers a worse prognosis.

People affected may have multiple scars on their abdomen due to repeated "emergency" operations.

In factitious disorder imposed on self, the affected person exaggerates or creates symptoms of illnesses in themselves to gain examination, treatment, attention, sympathy, and/or comfort from medical personnel. In some extreme cases, people suffering from Munchausen syndrome are highly knowledgeable about the practice of medicine and are able to produce symptoms that result in lengthy and costly medical analysis, prolonged hospital stays, and unnecessary operations. The role of "patient" is a familiar and comforting one, and it fills a psychological need in people with this syndrome. This disorder is distinct from hypochondriasis and other somatoform disorders in that those with the latter do not intentionally produce their somatic symptoms. Munchausen syndrome is distinct from other psychiatric disorders such as malingering in that Munchausen does not fabricate symptoms for material gain such as financial compensation, absence from work, or access to drugs.

Risk factors for developing factitious disorder include childhood traumas, growing up with parents/caretakers who were emotionally unavailable due to illness or emotional problems, a serious illness as a child, failed aspirations to work in the medical field, personality disorders, and low self-esteem. Factitious disorder is more common in men and is seen in young or middle-aged adults. Those with a history of working in healthcare are also at greater risk of developing it.

Arrhythmogenic Munchausen syndrome describes individuals who simulate or stimulate cardiac arrhythmias to gain medical attention.

A similar behavior called factitious disorder imposed on another has been documented in the parent or guardian of a child. The adult ensures that his or her child will experience some medical affliction, therefore compelling the child to suffer through treatments and spend a significant portion of their youth in hospitals. Furthermore, a disease may actually be initiated in the child by the parent or guardian. This condition is considered distinct from Munchausen syndrome. There is growing consensus in the pediatric community that this disorder should be renamed "medical abuse" to highlight the harm caused by the deception and to make it less likely that a perpetrator can use a psychiatric defense when harm is done.

MSbP is rare. A recent systematic study in Italy found that in a series of over 700 patients admitted to a pediatric ward, 4 cases met the diagnostic criteria for MSbP (0.53%). In this study, stringent diagnostic criteria were used, which required at least one test outcome or event that could not possibly have occurred without deliberate intervention by the MSbP person.

One study showed that in 93 percent of MSbP cases, the abuser is the mother or another female guardian or caregiver. This may be attributed to the prevalent socialization pattern that places females in the primary care-taking role. Of course, it could also be a gender trait rooted in genetics, as it is easy to see how females who seek attention as victims could gain an evolutionary advantage, while men seeking the same would be unfavoured for physical protection and mating. A psychodynamic model of this kind of maternal abuse exists.

MSbP may be more prevalent in the parents of those with a learning difficulty or mental incapacity, and as such the apparent patient could, in fact, be an adult.

Fathers and other male caregivers have been the perpetrators in only 7% of the cases studied. When they are not actively involved in the abuse, the fathers or male guardians of MSbP victims are often described as being distant, emotionally disengaged, and powerless. These men play a passive role in MSbP by being frequently absent from the home and rarely visiting the hospitalized child. Usually, they vehemently deny the possibility of abuse, even in the face of overwhelming evidence or their child's pleas for help.

Overall, male and female children are equally likely to be the victim of MSbP. In the few cases where the father is the perpetrator, however, the victim is three times more likely to be male.

Deaf-mute is a term which was used historically to identify a person who was either deaf using a sign language or both deaf and could not speak. The term continues to be used to refer to deaf people who cannot speak an oral language or have some degree of speaking ability, but choose not to speak because of the negative or unwanted attention atypical voices sometimes attract. Such people communicate using sign language. Some consider it to be a derogatory term if used outside its historical context; the preferred term today is simply "deaf".

The cause is unknown. Both environmental and genetic factors are believed to play a role. Risk factors include a history of child abuse or other stress-inducing event.

Obsessive–compulsive disorder affects about 2.3% of people at some point in their life. Rates during a given year are about 1.2% and it occurs worldwide. It is unusual for symptoms to begin after the age of thirty five and half of people develop problems before twenty. Males and females are affected about equally.

Genetically informed studies of the personality characteristics typical of individuals with psychopathy have found moderate genetic (as well as non-genetic) influences. On the PPI, fearless dominance and impulsive antisociality were similarly influenced by genetic factors and uncorrelated with each other. Genetic factors may generally influence the development of psychopathy while environmental factors affect the specific expression of the traits that predominate. A study on a large group of children found more than 60% heritability for "callous-unemotional traits" and that conduct problems among children with these traits had a higher heritability than among children without these traits.

A study by Farrington of a sample of London males followed between age 8 and 48 included studying which factors scored 10 or more on the PCL:SV at age 48. The strongest factors included having a convicted parent, being physically neglected, low involvement of the father with the boy, low family income, and coming from a disrupted family. Other significant factors included poor supervision, harsh discipline, large family size, delinquent sibling, young mother, depressed mother, low social class, and poor housing. There has also been association between psychopathy and detrimental treatment by peers. However, it is difficult to determine the extent of an environmental influence on the development of psychopathy because of evidence of its strong heritability.

Warning signs of the disorder include:

- A child who has one or more medical problems that do not respond to treatment or that follow an unusual course that is persistent, puzzling, and unexplained.

- Physical or laboratory findings that are highly unusual, discrepant with patient's presentation or history, or physically or clinically impossible.

- A parent who appears medically knowledgeable, fascinated with medical details and hospital gossip, appears to enjoy the hospital environment and expresses interest in the details of other patients' problems.

- A highly attentive parent who is reluctant to leave their child's side and who themselves seem to require constant attention.

- A parent who appears unusually calm in the face of serious difficulties in their child's medical course while being highly supportive and encouraging of the physician, or one who is angry, devalues staff and demands further intervention, more procedures, second opinions, and transfers to other more sophisticated facilities.

- The suspected parent may work in the health care field themselves or profess an interest in a health-related job.

- The signs and symptoms of a child's illness may lessen or simply vanish in the parent's absence (hospitalization and careful monitoring may be necessary to establish this causal relationship).

- A family history of similar or unexplained illness or death in a sibling.

- A parent with symptoms similar to their child's own medical problems or an illness history that itself is puzzling and unusual.

- A suspected emotionally distant relationship between parents; the spouse often fails to visit the patient and has little contact with physicians even when the child is hospitalized with a serious illness.

- A parent who reports dramatic, negative events, such as house fires, burglaries, or car accidents, that affect them and their family while their child is undergoing treatment.

- A parent who seems to have an insatiable need for adulation or who makes self-serving efforts for public acknowledgment of their abilities.

- A patient who inexplicably deteriorates whenever discharge is planned.

It is sometimes used to refer to other hearing people in jest, to chide, or to invoke an image of someone who refuses to employ common sense or who is unreliable. "Deaf and dumb", "semi-deaf" and "semi-mute" are other historic references to deaf people.

In the past "deaf-mute" was used to describe deaf people who used sign language, but in modern times, the term is frequently viewed as offensive and inaccurate. From antiquity (as noted in the Code of Hammurabi) until recent times, the terms "deaf-mute" and "deaf and dumb" were sometimes considered analogous to "stupid" by some hearing people.

The simple identity of "deaf" has been embraced by the community of signing deaf people since the foundations of public deaf education in the 18th century and remains the preferred term of reference or identity for many years. Within the deaf community there are some who prefer the term "Deaf" (upper-case D) to "deaf" (lower-case) as a description of their status and identity.

Classification as a deaf-mute has a particular importance in Jewish law. Because historically it was thought impossible to teach or communicate with them, deaf-mutes were not moral agents, and therefore were unable to own real estate, act as witnesses, or be punished for any crime. However, today when techniques for educating deaf people are known, they are no longer classed as such.