Ant venom is any of, or a mixture of, irritants and toxins inflicted by ants. Most ants spray or inject a venom, the main constituent of which is formic acid only in the case of subfamily Formicinae.

Insect sting allergy is the term commonly given to the allergic response of an animal in response to the bite or sting of an insect. Typically, insects which generate allergic responses are either stinging insects (wasps, bees, hornets and ants) or biting insects (mosquitoes, ticks). Stinging insects inject venom into their victims, whilst biting insects normally introduce anti-coagulants into their victims.

The great majority of insect allergic animals just have a simple allergic response – a reaction local to the sting site which appears as just a swelling arising from the release of histamine and other chemicals from the body tissues near to the sting site. The swelling, if allergic, can be helped by the provision of an anti-histamine ointment as well as an ice pack. This is the typical response for all biting insects and many people have this common reaction.

Mosquito allergy may result in a collection of symptoms called skeeter syndrome that occur after a bite. This syndrome may be mistaken for an infection such as cellulitis.

In anaphylactic patients the response is more aggressive leading to a systemic reaction where the response progresses from the sting site around the whole body. This is potentially something very serious and can lead to anaphylaxis, which is potentially life-threatening.

A bee sting is a sting from a bee (honey bee, bumblebee, sweat bee, etc.). The stings of most of these species can be quite painful, and are therefore keenly avoided by many people.

Bee stings differ from insect bites, and the venom or toxin of stinging insects is quite different. Therefore, the body's reaction to a bee sting may differ significantly from one species to another. In particular, bee stings are acidic, whereas wasp stings are alkali, so the body's reaction to a bee sting may be very different than to that of a wasp sting.

The most aggressive stinging insects are vespid wasps (including bald-faced hornets and other yellow jackets) and hornets (especially the Asian giant hornet). All of these insects aggressively defend their nests.

Although for most people a bee sting is painful but otherwise relatively harmless, in people with insect sting allergy, stings may trigger a dangerous anaphylactic reaction that is potentially deadly. Additionally, honey bee stings release pheromones that prompt other nearby bees to attack.

The histomorphologic appearance of insect bites is usually characterized by a wedge-shaped superficial dermal perivascular infiltrate consisting of abundant lymphocytes and scattered eosinophils. This appearance is non-specific, i.e. it may be seen in a number of conditions including:

- Drug reactions,

- Urticarial reactions,

- Prevesicular early stage of bullous pemphigoid, and

- HIV related dermatoses.

Feeding bites have characteristic patterns and symptoms, a function of the feeding habits of the offending pest and the chemistry of its saliva.

There are only rare examples of stinging ants. Some notable examples include "Solenopsis" (fire ants), "Pachycondyla", "Myrmecia" (bulldog ants), and "Paraponera" (bullet ants). In the case of fire ants, the venom consists of alkaloid and protein components. Stinging ants cause a cutaneous condition that is different from that caused by biting venomous ants. Particularly painful are stings from fire ants, although the bullet ant's sting is considered by some to be the most painful insect sting.

First aid for fire ant bites includes external treatments and oral medicines.

- External treatments: a topical steroid cream (hydrocortisone), or one containing "Aloe vera"

- Oral medicines: antihistamines

- Applying zinc oxide or calamine lotion .

Severe allergic reactions can be caused by ant stings in particular and venomous stings in general, including severe chest pain, nausea, severe sweating, loss of breath, serious swelling, fever, dizziness, and slurred speech; they can be fatal if not treated.

Many species of arthropods (insects, arachnids and others) regularly or occasionally bite or sting human beings. Insect saliva contains anticoagulants and enzymes that cause local irritation and allergic reactions. Insect venoms can be delivered by their stingers, which often are modified ovipositors, or by their mouthparts. Insect, spider and scorpion venom can cause serious injury or death. Dipterans account for the majority of insect bites, while hymenopterans account for the majority of stings. Among arachnids spider bites are the most common. Arthropods bite or sting humans for a number of reasons including feeding or defense. Arthropods are major vectors of human disease, with the pathogens typically transmitted by bites.

The majority of individuals who receive a sting from an insect experience local reactions. It is estimated that 5-10% of individuals will experience a generalized systemic reaction that can involve symptoms ranging from hives to wheezing and even anaphylaxis. In the United States approximately 40 people die each year from anaphylaxis due to stinging insect allergy. Potentially life-threatening reactions occur in 3% of adults and 0.4–0.8% of children.

This type of hives can occur right away, precisely after a pressure stimulus or as a deferred response to sustained pressure being enforced to the skin. In the deferred form, the hives only appear after about six hours from the initial application of pressure to the skin. Under normal circumstances, these hives are not the same as those witnessed with most urticariae. Instead, the protrusion in the affected areas is typically more spread out. The hives may last from eight hours to three days. The source of the pressure on the skin can happen from tight fitted clothing, belts, clothing with tough straps, walking, leaning against an object, standing, sitting on a hard surface, etc. The areas of the body most commonly affected are the hands, feet, trunk, abdomen, buttocks, legs and face. Although this appears to be very similar to dermatographism, the cardinal difference is that the swelled skin areas do not become visible quickly and tend to last much longer. This form of the skin disease is, however, rare.

Dermatographic urticaria (also known as dermatographism or "skin writing") is marked by the appearance of weals or welts on the skin as a result of scratching or firm stroking of the skin. Seen in 4–5% of the population, it is one of the most common types of urticaria, in which the skin becomes raised and inflamed when stroked, scratched, rubbed, and sometimes even slapped.

The skin reaction usually becomes evident soon after the scratching, and disappears within 30 minutes. Dermatographism is the most common form of a subset of chronic hives, acknowledged as "physical hives".

It stands in contrast to the linear reddening that does not itch seen in healthy people who are scratched. In most cases, the cause is unknown, although it may be preceded by a viral infection, antibiotic therapy, or emotional upset. Dermographism is diagnosed by taking a tongue blade and drawing it over the skin of the arm or back. The hives should develop within a few minutes. Unless the skin is highly sensitive and reacts continually, treatment is not needed. Taking antihistamines can reduce the response in cases that are annoying to the patient.

Scorpion stings are a cutaneous condition caused by the stinging of scorpions, usually resulting in pain, paresthesia, and variable swelling. The anatomical part of the scorpion that delivers the sting is called a "telson".

Most scorpion stings vary from small swelling to medically significant lesions in severity, with only a few able to cause severe allergic, neurotic or necrotic reactions. Only two species of scorpions can inflict stings which result in death of normal healthy humans: the Israeli deathstalker ("Leiurus quinquestriatus") and the "Brazilian yellow scorpion" (Tityus serrulatus). Antivenom exists for both species' stings.

Anaphylaxis typically presents many different symptoms over minutes or hours with an average onset of 5 to 30 minutes if exposure is intravenous and 2 hours if from eating food. The most common areas affected include: skin (80–90%), respiratory (70%), gastrointestinal (30–45%), heart and vasculature (10–45%), and central nervous system (10–15%) with usually two or more being involved.

Symptoms typically include generalized hives, itchiness, flushing, or swelling (angioedema) of the afflicted tissues. Those with angioedema may describe a burning sensation of the skin rather than itchiness. Swelling of the tongue or throat occurs in up to about 20% of cases. Other features may include a runny nose and swelling of the conjunctiva. The skin may also be blue tinged because of lack of oxygen.

The first step in treatment following a bee sting is removal of the stinger itself. The stinger should be removed as quickly as possible without regard to method: studies have shown the amount of venom delivered does not differ whether the sting is pinched or scraped off and even a delay of a few seconds leads to more venom being injected. Once the stinger is removed, pain and swelling should be reduced with a cold compress. A topical anesthetic containing benzocaine will kill pain quickly and menthol is an effective anti-itch treatment. Itching can also be relieved by antihistamine or by a steroid cream.

Many traditional remedies have been suggested for bee stings including damp pastes of tobacco, salt, baking soda, papain, toothpaste, clay, garlic, urine, onions, aspirin or even application of copper coins. As with jellyfish stings, ammonia and ammonia-containing liquids, such as window cleaner, are often suggested as a way to immediately cleanse the skin and remove excess venom, and sweat itself (which also contains small amounts of ammonia) may provide some small relief.

Bee venom is acidic, and these interventions are often recommended to neutralize the venom; however, neutralizing a sting is unlikely to be effective as the venom is injected under the skin and deep into the tissues, where a topically applied alkali is unable to reach, so neutralization is unlikely to occur. In any case, the amount of venom injected is typically very small (between 5 and 50 micrograms of fluid) and placing large amounts of alkali near the sting site is unlikely to produce a perfectly neutral pH to stop the pain. Many people do claim benefit from these home remedies but it is doubtful they have any real physical effect on how much a sting hurts or continues hurting. The effect is probably related to rubbing the area or the mind perceiving benefit. Furthermore, none of these interventions have been proven to be effective in scientific studies and a randomized trial of aspirin paste and topical ice packs showed that aspirin was not effective in reducing the duration of swelling or pain in bee and wasp stings, and significantly increased the duration of redness. The study concluded that ice alone is better treatment for bee and wasp stings than aspirin.

The sting may be painful for a few hours. Swelling and itching may persist for a week. The area should not be scratched as it will only increase the itching and swelling. If swelling persists for over a week or covers an area greater than , medical attention should be sought. Doctors often recommend a tetanus immunization. For about 2 percent of people, a hypersensitivity can develop after being stung, creating a more severe reaction when stung again later. This sensitisation may happen after a single sting, or after a series of stings where they reacted normally. A highly allergic person may suffer anaphylactic shock from certain proteins in the venom, which can be life-threatening and requires emergency treatment. People known to be highly allergic may carry around epinephrine (adrenaline) in the form of a self-injectable EpiPen for the treatment of an anaphylactic shock.

For patients who experience severe or life-threatening reactions to insect stings, allergy injections composed of increasing concentrations of naturally occurring venom may provide protections against future insect stings.

Many allergens such as dust or pollen are airborne particles. In these cases, symptoms arise in areas in contact with air, such as eyes, nose, and lungs. For instance, allergic rhinitis, also known as hay fever, causes irritation of the nose, sneezing, itching, and redness of the eyes. Inhaled allergens can also lead to increased production of mucus in the lungs, shortness of breath, coughing, and wheezing.

Aside from these ambient allergens, allergic reactions can result from foods, insect stings, and reactions to medications like aspirin and antibiotics such as penicillin. Symptoms of food allergy include abdominal pain, bloating, vomiting, diarrhea, itchy skin, and swelling of the skin during hives. Food allergies rarely cause respiratory (asthmatic) reactions, or rhinitis. Insect stings, food, antibiotics, and certain medicines may produce a systemic allergic response that is also called anaphylaxis; multiple organ systems can be affected, including the digestive system, the respiratory system, and the circulatory system. Depending on the rate of severity, it can cause a skin reactions, bronchoconstriction, swelling, low blood pressure, coma, and death. This type of reaction can be triggered suddenly, or the onset can be delayed. The nature of anaphylaxis is such that the reaction can seem to be subsiding, but may recur throughout a period of time.

Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity of the immune system to something in the environment that usually causes little or no problem in most people. These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis. Symptoms may include red eyes, an itchy rash, sneezing, a runny nose, shortness of breath, or swelling. Food intolerances and food poisoning are separate conditions.

Common allergens include pollen and certain food. Metals and other substances may also cause problems. Food, insect stings, and medications are common causes of severe reactions. Their development is due to both genetic and environmental factors. The underlying mechanism involves immunoglobulin E antibodies (IgE), part of the body's immune system, binding to an allergen and then to a receptor on mast cells or basophils where it triggers the release of inflammatory chemicals such as histamine. Diagnosis is typically based on a person's medical history. Further testing of the skin or blood may be useful in certain cases. Positive tests, however, may not mean there is a significant allergy to the substance in question.

Early exposure to potential allergens may be protective. Treatments for allergies include avoiding known allergens and the use of medications such as steroids and antihistamines. In severe reactions injectable adrenaline (epinephrine) is recommended. Allergen immunotherapy, which gradually exposes people to larger and larger amounts of allergen, is useful for some types of allergies such as hay fever and reactions to insect bites. Its use in food allergies is unclear.

Allergies are common. In the developed world, about 20% of people are affected by allergic rhinitis, about 6% of people have at least one food allergy, and about 20% have atopic dermatitis at some point in time. Depending on the country about 1–18% of people have asthma. Anaphylaxis occurs in between 0.05–2% of people. Rates of many allergic diseases appear to be increasing. The word "allergy" was first used by Clemens von Pirquet in 1906.

There are also a number of medical conditions that cause blisters. The most common are chickenpox, herpes, impetigo, and a form of eczema called dyshidrosis. Other, much rarer conditions that cause blisters include:

- Bullous pemphigoid: a skin disease that causes large, tightly filled blisters to develop, usually affecting people over the age of 60.

- Pemphigus: a serious skin disease in which blisters develop if pressure is applied to the skin; the blisters burst easily, leaving raw areas that can become infected.

- Dermatitis herpetiformis: a skin disease that causes intensely itchy blisters, usually on the elbows, knees, back and buttocks. The blisters usually develop in patches of the same shape and size on both sides of the body.

- Chronic bullous dermatosis: a disease that causes clusters of blisters on the face, mouth or genitals.

- Cutaneous radiation syndrome

- Epidermolysis bullosa

Intense rubbing can cause a blister, as can any friction on the skin if continued long enough. This kind of blister is most common after walking long distances or by wearing old or poorly fitting shoes. Blisters are most common on the hands and feet, as these extremities are susceptible while walking, running, or performing repetitive motions, such as joystick manipulation whilst playing certain video games, digging with a shovel, playing guitar, etc. Blisters form more easily on moist skin than on dry or soaked skin, and are more common in warm conditions. Less-aggressive rubbing over long periods of time may cause calluses to form rather than a blister. Both blisters and calluses can lead to more serious complications, such as foot ulceration and infection, particularly when sensation or circulation is impaired, as in the case of diabetes, neuropathy or peripheral artery disease (PAD).

Symptoms can take as long as 14 days after exposure to appear, and may include signs and symptoms commonly associated with hypersensitivity or infections.

- rashes

- itching

- joint pain (arthralgia), especially finger and toe joints

- fever, as high as 40 °C and usually appears before rash

- lymphadenopathy (swelling of lymph nodes), particularly near the site of injection, head and neck

- malaise

- hypotension (decreased blood pressure)

- splenomegaly (enlarged spleen)

- glomerulonephritis

- proteinuria

- hematuria

- shock

Serum sickness in humans is a reaction to proteins in antiserum derived from a non-human animal source, occurring 4–10 days after exposure. It is a type of hypersensitivity, specifically immune complex hypersensitivity (type III). The term serum sickness-like reaction (SSLR) is occasionally used to refer to similar illnesses that arise from the introduction of certain non-protein substances, such as penicillin. It was first characterized by Clemens von Pirquet and Béla Schick in 1906.

Causes of formication include normal states such as onset of menopause (i.e. hormone withdrawal). Other causes are medical conditions such as pesticide exposure, mercury poisoning, diabetic neuropathy, skin cancer, syphilis, Lyme disease or herpes zoster (shingles). Formication can be a result of stimulant intoxication (e.g. methamphetamines, cocaine) or alcohol withdrawal in alcoholics (i.e. delirium tremens), and is often accompanied by visual hallucinations of insects (formicanopia). It can also occur as a symptom of benzodiazepine withdrawal, withdrawal from medication such as SSRI/SNRI antidepressants and Tramadol; and as a side effect of opioid analgesics.

Formication is the medical term for a sensation that exactly resembles that of small insects crawling on (or under) the skin. It is one specific form of a set of sensations known as paresthesias, which also include the more common prickling, tingling sensation known as "pins and needles". Formication is a well documented symptom, which has numerous possible causes. The word is derived from "formica", the Latin word for ant.

Formication may sometimes be experienced as feelings of itchiness, tingling, pins and needles, burning, or even pain. When formication is perceived as itchiness, it may trigger the scratch reflex, and because of this, some people who are suffering from the sensation are at risk of causing skin damage through excessive scratching.

In some instances, static electricity can attract particulates to the skin and can also cause body hair to move, giving a sensation like insects crawling over the skin. However, in many cases no external trigger creates the sensation.

In rare cases, individuals become convinced that the sensation they are suffering is due to the presence of real insects on or under the skin. In these cases, patients have what is known as delusional parasitosis. They believe that their skin is inhabited by, or under attack by, small insects or similar parasites, despite repeated reassurances from physicians, pest control experts, and entomologists.

Thallium and its compounds are often highly toxic. Contact with skin is dangerous, and adequate ventilation should be provided when melting this metal. Many thallium(I) compounds are highly soluble in water and are readily absorbed through the skin. Exposure to them should not exceed 0.1 mg per m of skin in an 8-hour time-weighted average (40-hour work week). Thallium is a suspected human carcinogen.

Part of the reason for thallium's high toxicity is that, when present in aqueous solution as the univalent thallium(I) ion (Tl), it exhibits some similarities with essential alkali metal cations, particularly potassium (due to similar ionic radii). It can thus enter the body via potassium uptake pathways. Other aspects of thallium's chemistry differ strongly from that of the alkali metals, such as its high affinity for sulfur ligands. Thus, this substitution disrupts many cellular processes (for instance, thallium may attack sulfur-containing proteins such as cysteine residues and ferredoxins). Thallium's toxicity has led to its use (now discontinued in many countries) as a rat and ant poison.

Among the distinctive effects of thallium poisoning are hair loss (which led to its initial use as a depilatory before its toxicity was properly appreciated) and damage to peripheral nerves (victims may experience a sensation of walking on hot coals), although the loss of hair only generally occurs in low doses; in high doses the thallium kills before this can take effect. Thallium was once an effective murder weapon before its effects became understood and an antidote (Prussian blue) discovered. Indeed, thallium poisoning has been called the "poisoner's poison" since thallium is colorless, odorless and tasteless; its slow-acting, painful and wide-ranging symptoms are often suggestive of a host of other illnesses and conditions.

Black pod disease is caused by many different "Phytophthora spp." pathogens all expressing the same symptoms in cocoa trees ("Theobroma cacao"). This pathogen if left untreated can destroy all yields; annually the pathogen can cause a yield loss of up to 1/3 and up to 10% of total trees can be lost completely. With the value of the cocoa industry throughout the world being so large there are much research and control efforts that go into these "Phytophthora spp." pathogens.

This pathogen can be located anywhere on the cocoa trees but is most noted for the black mummified look it will give to the fruit of the cocoa tree. Staying ahead of the pathogen is the best means of control, the pathogen can be greatly reduced if leaf litter is not allowed to stay on the ground and if the pathogen gets out of hand chemical control can be used. This pathogen is mostly found in tropical areas where the cocoa trees are located and need rainfall in order to spread its spores.

Florida keratopathy, also known as Florida spots, is an eye condition characterized by the presence of multiple spots within both corneas. It is most commonly seen in dogs and cats, but is also rarely seen in horses and birds. The disease is found in the southeastern parts of the United States. In other parts of the world it is confined to tropics and subtropics, and it is known as tropical keratopathy.

Florida keratopathy appears as multiple cloudy opacities in the stromal layer of the cornea. The spots appear concentrated at the center and become more diffuse at the periphery. They can range in size from one to eight millimeters. There are no other symptoms, and there is no response to treatment with either anti-inflammatory or antimicrobial drugs. Histological analysis of affected corneas has found acid-fast staining organisms, suggesting Florida keratopathy may be caused by a type of mycobacterium. The disease may be induced by repeated stings to the eyes by the little fire ant, "Wasmannia auropunctata".