Author(s): Arthur Chang, T. Christy Hallett, David Kuai, Michael Yeh

Outside the United States, travelers may encounter unfamiliar substances that can be harmful to health. Folk remedies and foods may contain toxic plants or other ingredients that can be poisonous when ingested. Venomous animals can bite or sting, potentially causing pain and occasionally serious illness. Exposure to toxins, such as pesticides or carbon monoxide, may cause injury or death.

Local and regional poison centers can provide information and medical guidance in cases of suspected poisoning or other toxic exposures. They employ specialists knowledgeable about indigenous poisonous fauna and flora, as well as their available treatments. The World Health Organization offers a comprehensive list of poison centers and important contact information for many countries. Operating hours and availability to the general public may vary.

Complementary & Alternative Medicines

Herbal Medicine

International travelers who become ill may encounter herbal medicines or other local traditional folk remedies. Often touted as being natural and assumed to be safer than pharmaceutical products, many herbal remedies have not been studied in rigorous clinical trials. Herbs can be poisonous or interact with prescription medications to cause unpredictable adverse effects.

Plants can be misidentified, especially when gathered from the wild, and cause illness when used alone or in preparations (e.g., capsules, extracts, powders, teas). Even when properly identified and prepared, the concentrations of active substances in plants can differ depending on growing conditions (e.g., location, season), as well as harvesting and processing methods.

Contamination and adulteration of herbal medicinal products can pose serious threats to human health. Some herbal products have been found to contain high levels of toxic heavy metals such as arsenic, lead, or mercury. Herbal products can be adulterated by the addition of prescription drugs. Synthetic drugs have been found added to herbal medicines promoted as treatments for anxiety, diabetes, hypertension, insomnia, obesity, sexual dysfunction, or other ailments. International travelers should avoid using herbal products due to these potential health concerns. Furthermore, access to medical facilities may be limited and capability to treat these poisonings may vary from country to country.

Hallucinogens

Hallucinogens are psychoactive substances that can alter mood, thoughts, and perceptions without affecting consciousness. Many cultures use mind-altering substances from plants and fungi in religious ceremonies. In recent years, the use of psychoactive substances has been marketed to tourists in some destinations. Potential risks include drug interactions, threats to personal safety due to inebriation, and toxic effects. In addition to the two discussed below, hallucinogenic substances promoted to travelers include ibogaine, peyote cactus, psilocybin-containing mushrooms, and Salvia divinorum (“sage of the diviners”). Besides the potential health and safety risks associated with use of hallucinogens, their use also may be against the law in the country being visited.

Ayahuasca

Used in religious rituals in the Amazon region of South America (see Yellow Book chapter, Machu Picchu and the Sacred Valley), this beverage has been marketed to travelers as a cultural experience (e.g., ethnotourism) and treatment for depression. Made from the vine Banisteriopsis caapi and other plants, the exact ingredients can vary in depending on the location. Active substances include the hallucinogen N-N-dimethyltryptamine and beta-carboline alkaloids such as harmine and harmaline. Ayahuasca can inhibit the enzyme monoamine oxidase and lead to potentially dangerous interactions with certain medications. Ayahuasca ingestion has caused unpredictable and severe adverse effects, including agitation, hallucinations, rhabdomyolysis, seizures, and vomiting. Deaths have been reported following the use of ayahuasca.

Mad Honey

Mad honey has been used as a folk medicine in many areas around the world (e.g., Nepal, the Black Sea region of Turkey). Mad honey is honey contaminated with grayanotoxin, a chemical produced by Rhododendron plants. Used to treat diabetes, digestive problems, hypertension, and other medical conditions, it has also been promoted as a sexual enhancement. It is sometimes intentionally consumed for its intoxicating effects. Mad honey poisoning has been widely reported, with symptoms including ataxia, blurred or double vision, dizziness, drooling, headache, sweating, vomiting, and weakness. Grayanotoxin can cause bradycardia and other potentially dangerous arrythmias.

Environmental Toxins

Carbon Monoxide

Carbon monoxide (CO) is an odorless, colorless, and non-irritating gas produced during combustion of carbon-based fuels (e.g., charcoal, gasoline, propane). CO inhibits the molecular transport of oxygen from the blood to the tissues of the body. Manifestations associated with CO inhalation include dizziness, headache, nausea, vomiting, shortness of breath, loss of consciousness, and death. CO poisoning can have long-term neurologic effects even after removal from the exposure. Children and small pets often experience symptoms sooner than adults due to their higher respiratory rates. Deaths due to CO poisoning have been reported among international travelers staying in hotels and rented apartments.

CO poisoning risk can be minimized by not burning fuels from cars, generators, grills, heaters, or stoves in enclosed areas. Counsel travelers exhibiting manifestations of possible CO exposure to find a well-ventilated area and to seek immediate medical attention. Advise travelers that international lodgings could lack both CO and smoke alarms (standard smoke detectors do not detect CO) and to map out at least two forms of egress in case of emergency. Although small portable CO detectors are available for use while traveling, there is insufficient evidence to recommend for or against their routine use.

Chemical Irritants

In response to popular protests or civil unrest, law enforcement and military forces sometimes deploy chemical irritants, also known as crowd control agents, lacrimators, or “tear gas.” The intended purpose of these substances is to cause tearing of the eyes and pain without permanent injury, although cases of lasting disability and death have been reported. Chemical irritants can cause breathing problems (e.g., chest tightness, choking sensation, coughing, shortness of breath).

The most common chemical irritants include chloroacetophenone, chlorobenzylidenemalonitrile, and oleoresin capsicum, commonly called “pepper spray.” Adverse effects due to chemical irritants can be more severe following exposure to high concentrations or when these agents are used in areas where large groups of people cannot easily disperse. People can also be injured from being hit by pepper balls, tear gas canisters, or other projectiles fired into a crowd.

Advise travelers exposed to chemical irritants to leave the area immediately and to flush their eyes with copious amounts of clean water or saline solution, if available. Contact lens wearers should remove and not reuse their lenses, even if they are not disposable. Contaminated clothing should be removed but not pulled over the head, an action that may require cutting off the clothing. Exposed individuals should avoid touching contaminated areas of clothing, place all clothing in a sealed plastic bag to avoid further spread of the chemical irritant, and wash affected skin with soap and water. Immediate medical attention may be required for serious symptoms (e.g., difficulty breathing) or if symptoms persist. Contaminated clothing should be discarded, if possible, ideally sealed in two plastic bags. Clothing that cannot be discarded should be washed thoroughly with detergent, separate from other laundry. Chemical irritants can be difficult to remove from clothing and may persist despite multiple washings.

International travelers should be aware of areas where popular protests or other mass gatherings are planned or commonly occur. US citizens can enroll in the Department of State’s free Smart Traveler Enrollment Program to receive information from the local US embassy or consulate about safety and security concerns.

Herbicides, Pesticides & Rodenticides

Herbicides, pesticides, and rodenticides help reduce pests and the diseases they carry. All pesticides available for use in the United States are registered with the Environmental Protection Agency and evaluated for safety. Other countries, however, may use pesticides that have been deemed illegal, unsafe, or improperly labelled in the United States. Travelers visiting or working in rural areas may encounter agricultural insecticides or herbicides applied over large areas, often without proper personal protective equipment or other measures to prevent exposure. In urban areas, highly toxic substances, such as organophosphates, metal phosphides, and arsenic-containing compounds, may be used to control pests. There have been several cases of deaths among tourists in which pesticides used to fumigate hotel rooms were suspected to have played a role.

Children are at risk of household exposure to hazardous pesticides by tasting or placing objects into their mouths. A smaller dose can be toxic in children compared to an average adult. Advise travelers to be mindful about children playing in rooms treated with pesticides and to seek medical attention in cases of difficulty breathing, excessive drooling, nausea, vomiting, seizures, tremors, or an altered level of consciousness.

Food & Beverage Poisoning

Alcohol

Risks associated with consuming alcohol outside the United States include the possibility of drinking contaminated or adulterated products; this is particularly true in countries where regulations and standards for distilling and distributing alcohol are less strict. Homemade alcoholic beverages (“moonshine”), often produced under unsafe and unsanitary conditions, might contain contaminants, impurities, or unusually high levels of ethanol, thereby increasing the risk of alcohol poisoning.

Methanol, a toxic byproduct of ethanol production, is normally eliminated in commercial products but with improper distillation can remain (or even become more concentrated) in the final product. Methanol is also sometimes used to adulterate beverages in place of ethanol. Methanol consumption can lead to dizziness, headache, nausea, permanent visual loss, organ failure, and death. Advise travelers about the risks of consuming alcohol abroad, to only select reputable brands, and to drink in moderation (see the Yellow Book chapter, Substance Use & Substance Use Disorders).

Botulism

Botulism is a potentially deadly disease caused by a toxin produced by the bacterium Clostridium botulinum. Symptoms initially include blurred vision, difficulty speaking, and weakness, but can progress to paralysis. The illness may manifest and be transmitted multiple ways, including foodborne botulism, wound botulism, and infant botulism.

Most pertinent to international travel is foodborne botulism, caused by eating food contaminated with the botulinum toxin. Although the United States has food safety guidelines for canned and preserved foods, other countries may not. Preserved foods, including smoked fishes and other cured meats, can pose a risk if not stored at proper temperatures. Pickled or preserved foods also pose a risk if they do not contain the proper amounts of salt or acidity. Medical tourists (see the Yellow Book chapter, Medical Tourism) are at risk of iatrogenic botulism, a condition that results when too much botulinum toxin is injected to treat conditions such as chronic pain, excessive sweating, migraine headaches, muscle spasticity, obesity, or wrinkles.

Wound botulism can occur when bacteria enter a wound and produce the toxin, an exposure that can occur with use of intravenous drugs (e.g., heroin). This type of botulism can be prevented by properly caring for wounds and seeking medical attention if an infection is suspected. Infant botulism is caused by ingestion of bacteria spores by infants, often associated with consumption of contaminated honey or corn syrup.

Sedatives and Incapacitating Agents

Sedative drugs have been used to facilitate sexual assault or commit robberies by making victims unconscious or otherwise incapacitated (see Table 4-08). Advise travelers to avoid accepting or sharing drinks from strangers, to not leave drinks unattended, and to watch for signs of drink tampering, including a broken seal or different color/texture to the drink, or unusual tastes or smells. Common symptoms of poisoning with sedatives or incapacitating agents include drowsiness, dizziness, impaired judgement, and memory loss. Travelers should be aware of the above common scenarios and symptoms associated with intoxication and, if suspected, to seek immediate medical attention.

Foraging

Although foraging for wild edible plants and mushrooms can be a fun and interesting way to learn about nature and to find food in international destinations, it can also be dangerous. Edible plants and fungi in one country may have deadly lookalikes in another. Travelers who wish to forage should use region-specific field or foraging guides and should educate themselves on possible dangerous lookalikes. In addition to misidentification risks, there are sometimes legal issues surrounding foraging. For example, it can be illegal to forage for plants or mushrooms without permission from landowners and the act of harvesting itself can be illegal for certain plants and mushrooms.

Seafood

For a detailed review of seafood-associated toxicities (e.g., ciguatera fish poisoning, scombroid, neurotoxic shellfish poisoning), see the Yellow Book chapter, Food Poisoning from Marine Toxins.

Traditional Foods

Sampling local (thoroughly cooked) dishes is often a highlight of international travel. And while generally considered to be toxicologically safe, some types of traditional foods can be poisonous if not prepared or stored properly (see Table 4-09).

Zoonotic Exposures (Envenomations)

Animals use venom for defense or to subdue prey, and they deliver these toxic substances by biting or stinging. Venom often consists of complex mixtures of molecules that can affect a victim’s blood, muscle tissue, nervous system, or other organs.

Marine Animals

Cnidarians

Recreational activities in the ocean (e.g., scuba diving, snorkeling, swimming), can lead to encounters with marine animals that can sting or bite. Cnidarians include corals, hydroids (e.g., fire coral, Portuguese man o’ war), jellyfish, and sea anemones. These organisms have highly developed stinging structures (nematocysts) on their tentacles that can penetrate the skin and cause pain and irritation.

Many cnidarian stings cause painful and itching rashes but are not typically associated with severe illness. Seabather’s eruption is a rash caused by cnidarian larvae that become trapped (e.g., under a bathing suit). Fire coral is a frequent cause of stings among divers in the Caribbean. Jellyfish are encountered at beaches worldwide.

Australian Box Jellyfish

Certain types of cnidarian can cause life-threatening effects in humans. The Australian box jellyfish, Chironex fleckeri, can be found in the southwestern Pacific Ocean along the northern coast of Australia as well as Malaysia and New Guinea. They are most commonly encountered along shallow water beaches between October and June. The sting of an Australian box jellyfish can cause abnormal heart rhythms and cardiac arrest leading to death, with 77 fatalities recorded over the past century. Effects can occur rapidly, and many victims are unable to reach medical care in time. It is important to seek immediate medical attention without delay. Possible treatment includes use of box jellyfish antivenom and other therapies to limit cardiotoxicity.

Irukandji Jellyfish

Irukandji syndrome is a serious condition that can develop following the sting of the Irukandji jellyfish, Carukia barnesi, found along the northern coast of Australia. People stung by this jellyfish might have mild pain at first but can later develop a wide range of symptoms, including goosebumps, headache, waves of muscle spasms, restlessness, sweating, tachycardia, tachypnea, and a sense of doom. Many victims develop dangerously high hypertension, which can be followed by hypotension, reduced cardiac function, and pulmonary edema. Patients with Irukandji syndrome typically require urgent hospital treatment to control pain and blood pressure.

Portuguese Man O’War

The hydrozoan Physalia physalis, commonly known as the Portuguese man o’ war, is not a true jellyfish but has been reported to cause an Irukandji-like syndrome. The Portuguese man o’ war can be found throughout the Atlantic, Pacific, and Indian Oceans.

For the aforementioned marine animals, if tentacles remain adhered to the skin following a sting, they should be removed as soon as possible by washing with copious amounts of seawater. Tentacles can also be removed with forceps or the edge of a plastic card. Rinsing the area with fresh water can stimulate more nematocysts to discharge (thereby worsening the sting) and should be avoided. Vinegar is a common treatment for stings, and it may prevent further nematocyst firing in certain species found in tropical waters of the Indo-Pacific region. Vinegar application may, however, increase nematocyst discharge among species that live in the more temperate waters around the United States. Therefore, vinegar may be a reasonable first aid treatment depending on the location and species involved. Ice packs can provide some relief of pain for mild stings. Other folk remedies such as using urine or alcohol for irrigation are not recommended.

Hot water immersion is a treatment that can potentially halt the effects of some jellyfish venoms, including the Australian box jellyfish toxin that affects the heart. The technique involves soaking the affected body part in 113°F (45°C) water for approximately 20 minutes. Although the efficacy has not been well-proven, this may be a first aid treatment to consider if available.

Cone Snails

Cone snails are found throughout tropical waters of the Indo-Pacific region. They pose a hazard to divers or beachcombers who attempt to handle them, especially because many species have ornate, attractive shells. Cone snails have a long hollow proboscis that can inject venom using a dart-like tooth capable of penetrating a wetsuit. The venom contains proteins called conotoxins that can rapidly cause paralysis, coma, and death.

Fish

Certain types of fish (e.g., lionfish, stingrays, stonefish) possess sharp venomous spines that can injure humans. Hot-water immersion may limit the effects of venom from spiny fish. Many injured people require medical treatment for pain control, wound care, and removal of embedded foreign material.

Lionfish

Lionfish are native to the Indian and Pacific Oceans but have spread into the Caribbean Sea, Gulf of Mexico, and Mediterranean Sea. Their defensive spines can cause painful stings with redness and swelling, as well as other symptoms including nausea, muscle weakness, and sweating.

Stingrays

Stingray injuries typically occur when a human steps on or otherwise disturbs the animal, causing it to use its tail to sting and envenomate in defense. This can result in painful puncture wounds. Human deaths have been reported from stingray injuries, typically from deep penetrating wounds to the chest or abdomen. Stingers can break off and remain embedded in the wound, causing pain and possible infection. Manifestations of envenomation include cardiac arrhythmias and hypotension, dizziness, headache, fainting, muscle spasms, nausea, and vomiting.

Stonefish

Stonefish are venomous fish that can be found in shallow tropical waters of the western Pacific Ocean, Indian Ocean, and off the coast of East Africa. They have also been spotted in the Mediterranean Sea, where they may have been introduced. Swimmers, snorkelers, and scuba divers may encounter stonefish without being aware of their presence, due to their often-camouflaged appearance.  Stonefish stings cause severe pain, and a dark bluish discoloration of the wound and swelling that spread rapidly up the injured limb. Wounds can take months to heal. In addition, victims have experienced other effects of toxicity including abdominal pain and vomiting; cardiac arrhythmias, unstable blood pressure and heart failure; and confusion, headache, and life-threatening seizures. Because stonefish stings can cause life-threatening illness, advise travelers to seek immediate medical attention.

Blue-Ringed Octopus

The blue-ringed octopus, Hapalochlaena lunulata, can be found hidden in crevices in waters around Australia and the Indo-Pacific region. Scuba divers and snorkelers may encounter them underwater, although they have also been found by beachgoers in shallow water along the shore. The blue-ringed octopus displays bright blue rings when threatened and may bite humans when handled. Its salivary glands contain tetrodotoxin, a venom that can cause paralysis and death if not treated. Counsel travelers to avoid handling blue-ringed octopi.

Sea Urchins & Sea Stars

Sea urchins can cause severe puncture wounds, especially when stepped on. The venom on their spines can cause intense burning pain, redness, and swelling of the injured areas. Rare reports of illness following sea urchin envenomation have been reported, although the clinical effects are not well-documented. Sea urchin spines can be brittle and difficult to remove; retained spines can cause severe inflammation, infection, and scar tissue formation.
Although most sea stars are harmless, the crown-of-thorns starfish has long, sharp spines that contain toxins that can cause severe pain, nausea, vomiting, muscle paralysis, hemolysis, and coagulopathies. They are found in tropical coral reefs throughout the Pacific and Indian Oceans, from the Red Sea and East African coast to the Pacific coast of Central America, and are especially common near Australia. Scuba divers and snorkelers should avoid touching crown-of-thorns starfish because their spines can pierce through wetsuits.
Hot-water immersion can help limit the effects of sea urchin and starfish venoms. Medical attention may be needed to remove spines because they are often brittle and crumble easily. Travelers not up to date with tetanus vaccines may require a booster and, in some cases, antibiotics to prevent bacterial infections associated with puncture wounds in the marine environment.

Scorpions

Scorpions can be found on every continent except Antarctica but are most commonly seen in subtropical and tropical areas of the world. Scorpion stings often cause intense pain and redness, but venom from some species can cause severe illness, affecting the heart, nervous system, and other organs. Manifestations include agitation, arrhythmias, bleeding and other coagulation disorders, pancreatitis, uncontrollable muscle spasms, shock, and even death.

While most scorpion stings are not serious, medical attention may be needed for pain management and wound care, including preventive tetanus vaccine. Young children may be more likely to develop neurologic symptoms and need urgent treatment. People with severe symptoms of envenomation may require hospitalization and antivenoms, if available. Preventive measures to avoid scorpion stings include shaking out clothing and shoes before putting them on and wearing long-sleeved shirts and long pants when walking in areas known to contain scorpions.

Snakes

Many snake species possess venom used to immobilize or kill prey. In humans, snakebites can cause serious injury, disability, or even death. In 2019, an estimated 63,400 deaths worldwide were attributed to snakebites.

Although snakes can be found in many settings, simple preventive measures can greatly reduce the risk of snakebites. Counsel travelers to wear long pants, socks, and high boots when hiking in areas inhabited by venomous snakes and to inspect the ground before sitting down, especially at the base of a tree. Snakes are often found in vegetation along the banks of streams, rivers, and lakes. Counsel travelers to use a flashlight when walking outdoors at night and to not reach blindly into brush, tree branches, rocky ledges, holes, or even bags before checking visually for snakes and other venomous animals. Wearing heavy protective gloves when gathering firewood, not sleeping on the ground, and carefully shaking out bedding material, shoes, and clothing before use also may reduce risk. Mosquito nets may prevent snakebites and should be tucked securely under sleeping bags. When appropriate, travelers should work with a knowledgeable local guide familiar with local snake species.

First aid recommendations vary depending on the type of snake involved; for advice, consult local qualified healthcare providers with knowledge about the types of snakes that are in the area. Photographs of the snake may aid in identification, although untrained persons should not attempt to capture the snake. Tourniquets that cut off blood flow, cutting the skin surrounding fang marks, attempts to suck out the venom, topical treatments, herbs, and other folk remedies are not recommended. Immobilization of a bitten arm or leg in an elevated and extended position with a splint may be helpful. Pressure immobilization bandages to limit lymphatic drainage may be considered for neurotoxic venom.

Access to prompt medical treatment is the most important measure to limit the extent of injury and illness following a snakebite, and delayed access to care can be life-threatening. Treatment often requires antivenom, which could be difficult to obtain in remote areas. When traveling in areas known to have venomous snakes, it is prudent to obtain information about the location of the closest medical facility, availability of antivenom, and resources for transportation to a larger hospital if needed.

Elapidae

Snakes in the Elapidae family include cobras, mambas, and coral snakes found in subtropical and tropical areas throughout the world. They possess venom associated with neurotoxic effects, including blurred vision, numbness and tingling, muscle paralysis, difficulty swallowing, and impaired breathing.

Viperidae

Snakes in the family Viperidae, commonly known as vipers or viperids, are widely found throughout the world except in Australia, Hawaii, Madagascar, and other isolated islands. They have hemotoxic and myotoxic venoms. Hemotoxic venom interferes with blood clotting, which can cause abnormal bleeding. Myotoxic venom effects cause extensive tissue and muscle damage at the site of the bite.

Sea Snakes

Sea snakes are found in tropical and temperate areas of the Indian and Pacific Oceans. The yellow-bellied sea snake, Pelamis platurus, has also been found along the eastern Pacific Coast of Central and South America. All 52 known species of sea snakes are venomous, and human deaths from bites have been reported. Sea snake bites are often painless or cause minimal pain but can be very dangerous. Victims typically experience neurologic symptoms (e.g., difficulty breathing, difficulty swallowing, muscle spasms, paralysis), which can be life-threatening. Damage to muscle tissue can be painful and extensive. Liver and kidney damage has been reported.

Spiders

Most encounters with spiders are harmless and do not result in injury or illness. Some spiders, however, capture and immobilize prey using venom; these species may potentially bite humans. Spiders are shy and typically do not attack humans without provocation but may bite in self-defense if disturbed. Reports of spider bites are often unreliable because people commonly mistake skin wounds and infections for spider bites, even if no spider was seen.

Australian Funnel Web Spiders

Australian funnel web spiders are considered some of the most poisonous spiders worldwide, implicated in human deaths. All species in the family Atracidae are native to Australia. They live in underground burrows and crevices. Funnel web spider bites can cause involuntary muscle twitching and spasms, sweating, rapid and irregular heart rate, tearing, drooling, vomiting, and difficulty breathing. First aid includes use of a pressure immobilization bandage and immediate transport to the nearest hospital. Timely use of antivenom can limit the severity of symptoms after a bite. 

Latrodectus Species

Envenomation from widow spiders (genus Latrodectus) has been known to cause severe symptoms. Widow spiders are found in temperate and tropical areas around the world; they hide in crevices, stone walls, wood piles, and tight spaces in buildings. Typically shy and nocturnal, widow spiders bite when disturbed. Their venom can cause severe painful muscle cramps and spasms, along with restlessness, sweating, vomiting, and other symptoms. Although death is rare, symptoms can be temporarily debilitating, and medical treatment for pain control, wound care, including tetanus vaccine, may be needed. Antivenoms may be available in some areas for treating bites from certain widow spider species, although they are not always needed.

Loxosceles Species

Bites from recluse spiders (genus Loxoceles) can cause wounds with local tissue damage. There are more than 200 species distributed widely throughout the world, including North and South America, Europe, Asia, and Australia. They can be found in hidden crevices of human homes, under stones, in firewood, tree bark, or other tight spaces. The bitten area may become red at first, followed by blistering, bleeding, dark discoloration, and ulcer formation. Although rare, human deaths have been reported from recluse spider bites as a result of severe hemolysis or hypersensitivity reactions. People who develop wounds or other symptoms of illness after a recluse spider bite should seek immediate medical attention.

Phoneutria Species

Armed, banana, or wandering spiders, Phoneutria, are found in Brazil and other parts of South America. They can be found in human dwellings as well as banana plantations, where farm workers may be at higher risk of being bitten. In addition to pain and redness at the bite site, pain can spread to the entire body. Phoneutria envenomation can also cause dizziness, nausea, restlessness, tachycardia, vomiting, salivation, sweating, and vision changes due to neurotoxins in the venom. Deaths are rare but have been reported to occur within hours, typically due to inability to breathe.

Tarantulas

Tarantula bites may be painful, but their venoms typically do not cause serious illness. Some tarantulas defend themselves by releasing small urticating hairs that can penetrate the skin and cause itching and inflammation. Urticating hairs that land in the eyes can cause more serious problems and may need to be surgically removed.