Human milk sickness is uncommon today in the United States. Current practices of animal husbandry generally control the pastures and feed of cattle, and the pooling of milk from many producers lowers the risk of tremetol present in dangerous amounts. The poison tremetol is not inactivated by pasteurization. Although extremely rare, milk sickness can occur if a person drinks contaminated milk or eats dairy products gathered from a single cow or from a smaller herd that has fed on the white snakeroot plant. There is no cure, but treatment is available.

Milk sickness, also known as tremetol vomiting or, in animals, as trembles, is a kind of poisoning, characterized by trembling, vomiting, and severe intestinal pain, that affects individuals who ingest milk, other dairy products, or meat from a cow that has fed on white snakeroot plant, which contains the poison tremetol.

Although very rare today, milk sickness claimed thousands of lives among migrants to the Midwest in the early 19th century in the United States, especially in frontier areas along the Ohio River Valley and its tributaries where white snakeroot was prevalent. New settlers were unfamiliar with the plant and its properties. A notable victim was Nancy Hanks Lincoln, the mother of Abraham Lincoln, who died in 1818. Nursing calves and lambs may have died from their mothers' milk contaminated with snakeroot, although the adult cows and sheep showed no signs of poisoning. Cattle, horses, and sheep are the animals most often poisoned.

Anna Pierce Hobbs Bixby, called Dr. Anna on the frontier, is credited today by the American medical community with having identified white snakeroot as the cause of the illness. Told about the plant's properties by an elderly Shawnee woman she befriended, Bixby did testing to observe and document evidence. She wrote up her findings to share the discovery in the medical world. The Shawnee woman's name has been lost to history.

Sweating sickness, also known as "English sweating sickness" or "English sweate" (), was a mysterious and highly contagious disease that struck England, and later continental Europe, in a series of epidemics beginning in 1485. The last outbreak occurred in 1551, after which the disease apparently vanished. The onset of symptoms was dramatic and sudden, death often occurring within hours. Although its cause remains unknown, it has been suggested that an unknown species of hantavirus was responsible for the outbreak.

The cause is the most mysterious aspect of the disease. Commentators then and now put much blame on the generally poor sanitation, sewage and contaminated water supplies of the time, which might have harboured the source of infection. The first outbreak at the end of the Wars of the Roses means that it may have been brought over from France by the French mercenaries whom Henry VII used to gain the English throne. However, the "Croyland Chronicle" mentions that Thomas Stanley, 1st Earl of Derby used the "sweating sickness" as an excuse not to join with Richard III's army prior to the Battle of Bosworth.

Relapsing fever has been proposed as a possible cause. This disease, which is spread by ticks and lice, occurs most often during the summer months, as did the original sweating sickness. However, relapsing fever is marked by a prominent black scab at the site of the tick bite and a subsequent skin rash.

Noting symptom overlap with hantavirus pulmonary syndrome, several scientists proposed an unknown hantavirus as the cause. A critique of this hypothesis included the argument that, whereas sweating sickness was thought to be transmitted from human to human, hantaviruses are rarely spread in this way. However, infection via human-to-human contact has been proven in hantavirus outbreaks in Argentina.

The following factors increase some people's susceptibility to airsickness:

- Fatigue, stress, and anxiety, are some factors that can increase susceptibility to motion sickness of any type.

- The use of alcohol, drugs, and medications may also contribute to airsickness.

- Additionally, airsickness is more common in women (especially during menstruation or pregnancy), young children, and individuals prone to other types of motion sickness.

- Although airsickness is uncommon among experienced pilots, it does occur with some frequency in student pilots.

Travelers who are susceptible to motion sickness can minimize symptoms by:

- Choosing a window seat with a view of the ground or of lower clouds, such that motion can be detected. This will not work if the plane is flown in the clouds for a long duration.

- Choosing seats with the smoothest ride in regards to pitch (the seats over the wings in an airplane). (This may not be sufficient for sensitive individuals who need to see ground movement)

- Sitting facing forward while focusing on distant objects rather than trying to read or look at something inside the airplane.

- Eating dry crackers, olives or suck on a lemon, to dry out the mouth, lessening nausea.

- Drinking a carbonated beverage.

Morning sickness may be an evolved trait that protects the baby against toxins ingested by the mother. Evidence in support of this theory includes:

- Morning sickness is very common among pregnant women, which argues in favor of its being a functional adaptation and against the idea that it is a pathology.

- Fetal vulnerability to toxins peaks at around 3 months, which is also the time of peak susceptibility to morning sickness.

- There is a good correlation between toxin concentrations in foods, and the tastes and odors that cause revulsion.

Women who have "no" morning sickness are more likely to miscarry. This may be because such women are more likely to ingest substances that are harmful to the fetus.

In addition to protecting the fetus, morning sickness may also protect the mother. A pregnant woman's immune system is suppressed during pregnancy, presumably to reduce the chances of rejecting tissues of her own offspring. Because of this, animal products containing parasites and harmful bacteria can be especially dangerous to pregnant women. There is evidence that morning sickness is often triggered by animal products including meat and fish.

If morning sickness is a defense mechanism against the ingestion of toxins, the prescribing of anti-nausea medication to pregnant women may have the undesired side effect of causing birth defects or miscarriages by encouraging harmful dietary choices.

Although the occurrence of DCS is not easily predictable, many predisposing factors are known. They may be considered as either environmental or individual.

Decompression sickness and arterial gas embolism in recreational diving are associated with certain demographic, environmental, and dive style factors. A statistical study published in 2005 tested potential risk factors: age, gender, body mass index, smoking, asthma, diabetes, cardiovascular disease, previous decompression illness, years since certification, dives in the last year, number of diving days, number of dives in a repetitive series, last dive depth, nitrox use, and drysuit use. No significant associations with risk of decompression sickness or arterial gas embolism were found for asthma, diabetes, cardiovascular disease, smoking, or body mass index. Increased depth, previous DCI, larger number of consecutive days diving, and being male were associated with higher risk for decompression sickness and arterial gas embolism. Nitrox and drysuit use, greater frequency of diving in the past year, increasing age, and years since certification were associated with lower risk, possibly as indicators of more extensive training and experience.

The following environmental factors have been shown to increase the risk of DCS:

- the magnitude of the pressure reduction ratio – a large pressure reduction ratio is more likely to cause DCS than a small one.

- repetitive exposures – repetitive dives within a short period of time (a few hours) increase the risk of developing DCS. Repetitive ascents to altitudes above within similar short periods increase the risk of developing altitude DCS.

- the rate of ascent – the faster the ascent the greater the risk of developing DCS. The US Navy Dive Manual indicates that ascent rates greater than about when diving increase the chance of DCS, while recreational dive tables such as the Bühlmann tables require an ascent rate of with the last taking at least one minute. An individual exposed to a rapid decompression (high rate of ascent) above has a greater risk of altitude DCS than being exposed to the same altitude but at a lower rate of ascent.

- the duration of exposure – the longer the duration of the dive, the greater is the risk of DCS. Longer flights, especially to altitudes of and above, carry a greater risk of altitude DCS.

- underwater diving before flying – divers who ascend to altitude soon after a dive increase their risk of developing DCS even if the dive itself was within the dive table safe limits. Dive tables make provisions for post-dive time at surface level before flying to allow any residual excess nitrogen to outgas. However, the pressure maintained inside even a pressurized aircraft may be as low as the pressure equivalent to an altitude of above sea level. Therefore, the assumption that the dive table surface interval occurs at normal atmospheric pressure is invalidated by flying during that surface interval, and an otherwise-safe dive may then exceed the dive table limits.

- diving before travelling to altitude – DCS can occur without flying if the person moves to a high-altitude location on land immediately after diving, for example, scuba divers in Eritrea who drive from the coast to the Asmara plateau at increase their risk of DCS.

- diving at altitude – diving in water whose surface altitude is above — for example, Lake Titicaca is at — without using versions of decompression tables or dive computers that are modified for high-altitude.

The cause of morning sickness is unknown. While some have claimed it to be due to psychological reasons, this is not supported by evidence.

Nausea and vomiting may also occur with molar pregnancy.

All divers should be free of conditions and illnesses that would negatively impact their safety and well-being underwater. The diving medical physician should be able to identify, treat and advise divers about illnesses and conditions that would cause them to be at increased risk for a diving accident.

Some reasons why a person should not be allowed to dive are as follows:

- Disorders that lead to altered consciousness: conditions that produce reduced awareness or sedation from medication, drugs, marijuana or alcohol; fainting, heart problems and seizure activity.

- Disorders that substantially increase the risk of barotrauma injury conditions or diseases that are associated with air trapping in closed spaces, such as sinuses, middle ear, lungs and gastrointestinal tract. Severe asthma is an example.

- Disorders that may lead to erratic and irresponsible behavior: included here would be immaturity, psychiatric disorders, diving while under the influence of medications, drugs and alcohol or any medical disorder that results in cognitive defects.

Conditions that may increase risk of diving disorders:

- Patent foramen ovale

- Diabetes mellitus — No serious problems should be expected during dives due to hypoglycaemia in divers with well-controlled diabetes. Long-term complications of diabetes should be considered and may be a contrindication.

- Asthma

Conditions considered temporary reasons to suspend diving activities:

- Pregnancy—It is unlikely that literature research can establish the effect of scuba diving on the unborn human fetus as there is insufficient data, and women tend to comply with the diving industry recommendation not to dive while pregnant.

Some of the drugs associated with serum sickness are:

- allopurinol

- barbiturates

- captopril

- cephalosporins

- griseofulvin

- penicillins

- phenytoin

- procainamide

- quinidine

- streptokinase

- sulfonamides

- rituximab

- ibuprofen

- infliximab

Ascending slowly is the best way to avoid altitude sickness. Avoiding strenuous activity such as skiing, hiking, etc. in the first 24 hours at high altitude reduces the symptoms of AMS. Alcohol and sleeping pills are respiratory depressants, and thus slow down the acclimatization process and should be avoided. Alcohol also tends to cause dehydration and exacerbates AMS. Thus, avoiding alcohol consumption in the first 24–48 hours at a higher altitude is optimal.

Taravana is a disease often found among Polynesian island natives who habitually dive deep without breathing apparatus many times in close succession, usually for food or pearls. These free-divers may make 40 to 60 dives a day, each of 30 or 40 metres (100 to 140 feet).

Taravana seems to be decompression sickness. The usual symptoms are vertigo, nausea, lethargy, paralysis and death. The word "taravana" is Tuamotu Polynesian for "to fall crazily".

Taravana is also used to describe someone who is "crazy because of the sea".

Allergenic extracts, hormones and vaccines can also cause serum sickness.

The most common hypothesis for the cause of motion sickness is that it functions as a defense mechanism against neurotoxins. The area postrema in the brain is responsible for inducing vomiting when poisons are detected, and for resolving conflicts between vision and balance. When feeling motion but not seeing it (for example, in a ship with no windows), the inner ear transmits to the brain that it senses motion, but the eyes tell the brain that everything is still. As a result of the discordance, the brain will come to the conclusion that the individual is hallucinating and further conclude that the hallucination is due to poison ingestion. The brain responds by inducing vomiting, to clear the supposed toxin. Treisman's indirect argument has recently been questioned via an alternative direct evolutionary hypothesis, as well as modified and extended via a direct poison hypothesis. The direct evolutionary hypothesis essentially argues that there are plausible means by which ancient real or apparent motion could have contributed directly to the evolution of aversive reactions, without the need for the co-opting of a poison response as posited by Treisman. Nevertheless, the direct poison hypothesis argues that there still are plausible ways in which the body's poison response system may have played a role in shaping the evolution of some of the signature symptoms that characterize motion sickness.

An alternative theory, also known as the Nystagmus Hypothesis, has been proposed based on stimulation of the vagus nerves resulting from the stretching or traction of extra-ocular muscles co-occurring with eye movements caused by vestibular stimulation. There are three critical aspects to the theory: first is the close linkage between activity in the vestibular system, i.e., semicircular canals and otolith organs, and a change in tonus among various of each eye's six extra-ocular muscles. Thus, with the exception of voluntary eye movements, the vestibular and oculomotor systems are thoroughly linked. Second is the operation of Sherrington's Law describing reciprocal inhibition between agonist-antagonist muscle pairs, and by implication the stretching of extraocular muscle that must occur whenever Sherrington's Law is made to fail, thereby causing an unrelaxed (contracted) muscle to be stretched. Finally there is the critical presence of afferent output to the Vagus nerves as a direct result of eye muscle stretch or traction. Thus, 10th nerve stimulation resulting from eye muscle stretch is proposed as the cause of motion sickness. The theory explains why labyrinthine defective individuals are immune to motion sickness; why symptoms emerge when undergoing various body-head accelerations; why combinations of voluntary and reflexive eye movements may challenge the proper operation of Sherrington's Law, and why many drugs that suppress eye movements also serve to suppress motion sickness symptoms.

Pre-acclimatization is when the body develops tolerance to low oxygen concentrations before ascending to an altitude. It significantly reduces risk because less time has to be spent at altitude to acclimatize in the traditional way. Additionally, because less time has to be spent on the mountain, less food and supplies have to be taken up. Several commercial systems exist that use altitude tents, so called because they mimic altitude by reducing the percentage of oxygen in the air while keeping air pressure constant to the surroundings.

Milk allergy typically presents in the first year of life. The majority of children outgrow milk allergy by the age of ten years. One large clinical trial reported resolutions of 19% by age 4 years, 42% by age 8 years, 64% by age 12 years, and 79% by 16 years. Children are be able to tolerate milk as an ingredient in baked goods relative to liquid milk. Resolution was more likely if baseline serum IgE was lower, or if IgE-mediated allergy was absent so that all that was present was cell-mediated, non-IgE allergy.

People with confirmed cow's milk allergy may also demonstrate an allergic response to beef, moreso to rare beef versus well-cooked beef. The offending protein appears to be bovine serum albumin. This is not the same beef allergy that is seen primarily in the southeastern United States, triggered by being bitten by a Lone Star tick.

Milk allergy has consequences. In a U.S. government diet and health surveys conducted in 2007-2010, 6,189 children ages 2-17 years were assessed. For those classified as cow's milk allergic at the time of the survey, mean weight, height and body-mass index were significantly lower than their non-allergic peers. This was not true for children with other food allergies. Diet assessment showed a significant 23% reduction of calcium intake and near-significant trends for lower vitamin D and total calorie intake.

One common suggestion is to simply look out of the window of the moving vehicle and to gaze towards the horizon in the direction of travel. This helps to re-orient the inner sense of balance by providing a visual reaffirmation of motion.

In the night, or in a ship without windows, it is helpful to simply close one's eyes, or if possible, take a nap. This resolves the input conflict between the eyes and the inner ear. Napping also helps prevent psychogenic effects (i.e. the effect of sickness being magnified by thinking about it).

Fresh, cool air can also relieve motion sickness slightly, although it is likely this is related to avoiding foul odors which can worsen nausea.

While playing computer games, and mainly in first-person shooter games, some cases of simulation sickness can be resolved by changing the field of view in the game. Some games have a default setting which places a player's vision a small distance ahead of the actual object controlled, which will most likely trigger simulation sickness.

In most places, contamination comes from a variety of sources (non-point source pollution). In a few it is primarily pollution from a single industrial source. The more immediate threat is from locations where high concentrations of toxic or pathogenic pollutants are present, but lower concentrations of less immediately harmful contaminants can have a longer term influence on the diver's health. Three major categories of contamination can cause health and safety problems for divers. These are biological, chemical and radioactive materials.

The risks from hazardous materials are generally proportional to dosage - exposure time and concentration, and the effects of the material on the body. This is particularly the case with chemical and radiological contaminants.There may be a threshold limit value which will not usually produce ill effects over long term exposure. Others may have a cumulative effect.

The United Nations identification numbers for hazardous materials classifies hazardous materials under 9 categories:

1. Explosives

2. Gases, which may be compressed, liquified or dissolved under pressure

3. Flammable liquids

4. Flammable solids

5. Oxidising agents

6. Poisonous and infectious substances

7. Radioactive substances

8. Corrosive substances

9. Miscellaneous hazardous substances

A contaminant may be classed under one or more of these categories.

Poisonous substances are also classified in 9 categories:

1. Irritants

2. Simple asphyxiants

3. Blood asphyxiants

4. Tissue asphyxiants

5. Respiratory paralysers

6. Liver and kidney toxins

7. Substances that affect the muscles (myotoxins)

8. Substances that affect bone marrow

9. Substances tha interfere with nerve function (neurotoxins)

Incidence and prevalence are terms commonly used in describing disease epidemiology. Incidence is newly diagnosed cases, which can be expressed as new cases per year per million people. Prevalence is the number of cases alive, expressible as existing cases per million people during a period of time. Milk allergies are usually observed in infants and young children, and often disappear with age (see Prognosis), so prevalence of egg allergy may be expressed as a percentage of children under a set age. Milk allergy affects between 2% and 3% of infants in developed countries. This estimate is for antibody-based allergy; prevalence of allergy based on cellular immunity is unknown.

For all age groups, a review of fifty studies conducted in Europe estimated 6.0% for self-reported milk allergy and 0.6% for confirmed. National survey data in the United States collected 2005-2006 showed that from age six and older, the prevalence of serum IgE confirmed milk allergy was under 0.4%.

A vaccine is available, called "Chinese Live Attenuated EIA vaccine", developed in China and widely used there since 1983. Another attenuated live virus vaccine is in development in the United States.

Reuse of syringes and needles is a risk factor for transfer of the disease. Currently in the United States, all horses that test positive must be reported to federal authorities by the testing laboratory. EIA-positive horses are infected for life. Options for the horse include sending the horse to a recognized research facility, branding the horse and quarantining it at least 200 yards from other horses for the rest of its life, and euthanizing the horse. Very few quarantine facilities exist, which usually leads to the option of euthanizing the horse. The Florida Research Institute for Equine Nurturing, Development and Safety (a.k.a. F.R.I.E.N.D.S.) is one of the largest such quarantine facilities and is located in south Florida.

The horse industry and the veterinary industry strongly suggest that the risks posed by infected horses, even if they are not showing any clinical signs, are enough of a reason to impose such stringent rules. The precise impacts of the disease on the horse industry are unknown.

As of 2010 it caused around 9,000 deaths, down from 34,000 in 1990. As of 2000, the disability-adjusted life-years (9 to 10 years) lost due to sleeping sickness are 2.0 million. From 2010-2014, there was an estimated 55 million people at risk for "gambiense" African Trypanosomiasis and over 6 million people at risk for "rhodesiense" African Trypanosomiasis. In 2014, the World Health Organization reported 3,797 cases of Human African Trypanosomiasis when the predicted number of cases were to be 5,000. The number of total reported cases in 2014 is an 86% reduction to the total number of cases reported in 2000.

The disease has been recorded as occurring in 37 countries, all in sub-Saharan Africa. It occurs regularly in southeast Uganda and western Kenya, and killed more than 48,000 Africans in 2008. The Democratic Republic of the Congo is the most affected country in the world, accounting for 75% of the "Trypanosoma brucei gambiense" cases. The population at risk being about 69 million with one third of this number being at a 'very high' to 'moderate' risk and the remaining two thirds at a 'low' to 'very low' risk. The number of people being affected by the disease has declined. At this rate, sleeping sickness elimination is a possibility. The World Health Organization plans to eradicate sleeping sickness by the year 2020.

The most common food allergens account for about 90% of all allergic reactions; in adults they include shellfish, peanuts, tree nuts, fish, and egg. In children, they include milk, eggs, peanuts, and tree nuts. Six to 8% of children under the age of three have food allergies and nearly 4% of adults have food allergies.

For reasons not entirely understood, the diagnosis of food allergies has apparently become more common in Western nations recently. In the United States, food allergy affects as many as 5% of infants less than three years of age and 3% to 4% of adults. A similar prevalence is found in Canada.

About 75% of children who have allergies to milk protein are able to tolerate baked-in milk products, i.e., muffins, cookies, cake, and hydrolyzed formulas.

About 50% of children with allergies to milk, egg, soy, peanuts, tree nuts, and wheat will outgrow their allergy by the age of 6. Those who are still allergic by the age of 12 or so have less than an 8% chance of outgrowing the allergy.

Peanut and tree nut allergies are less likely to be outgrown, although evidence now shows that about 20% of those with peanut allergies and 9% of those with tree nut allergies will outgrow them.

In Japan, allergy to buckwheat flour, used for soba noodles, is more common than peanuts, tree nuts or foods made from soy beans.

Corn allergy may also be prevalent in many populations, although it may be difficult to recognize in areas such as the United States and Canada where corn derivatives are common in the food supply.

Equine infectious anemia or equine infectious anaemia (EIA), also known by horsemen as swamp fever, is a horse disease caused by a retrovirus and transmitted by bloodsucking insects. The virus ("EIAV") is endemic in the Americas, parts of Europe, the Middle and Far East, Russia, and South Africa. The virus is a lentivirus, like human immunodeficiency virus (HIV). Like HIV, EIA can be transmitted through blood, milk, and body secretions.

Transmission is primarily through biting flies, such as the horse-fly and deer-fly. The virus survives up to 4 hours in the vector (epidemiology). Contaminated surgical equipment and recycled needles and syringes, and bits can transmit the disease. Mares can transmit the disease to their foals via the placenta.

The risk of transmitting the disease is greatest when an infected horse is ill, as the blood levels of the virus are then highest.