Arsenic poisoning produces different symptoms depending on whether exposure is sudden or gradual. A single large dose causes violent gastrointestinal distress within 30 minutes to several hours, while long-term exposure to lower levels leads to skin changes, nerve damage, and increased cancer risk that can take months or years to develop. Recognizing the difference matters because chronic exposure is far more common and easier to miss.
Acute Symptoms: The First Hours
A large dose of arsenic hits the gut first. The earliest signs, appearing within 30 minutes to a few hours, include burning of the lips, a feeling of tightness in the throat, severe abdominal pain, and nausea. Many people notice a metallic or garlic-like taste in the mouth and intense thirst. Vomiting and profuse, watery diarrhea follow quickly, sometimes becoming bloody as arsenic damages the lining of the stomach and intestines. A distinctive garlic odor on the breath and skin is one of the more specific clues that arsenic is involved.
The fluid loss from vomiting and diarrhea can become dangerous on its own, leading to a rapid heart rate (often the first cardiovascular warning sign), dangerously low blood pressure, and shock. In severe cases, arsenic also affects the heart’s electrical system, causing irregular rhythms that can be fatal. The brain may be affected too: headache, confusion, delirium, hallucinations, seizures, and loss of consciousness are all possible with a large enough dose.
How Arsenic Damages Cells
Arsenic is toxic because it sabotages your cells’ ability to produce energy. It binds to key enzymes involved in converting food into fuel and mimics phosphorus in critical chemical reactions. When arsenic slips into the spot normally occupied by phosphorus, it destabilizes high-energy molecules like ATP, your cells’ main energy currency. The result is that cells essentially run out of power, which explains why arsenic can damage so many different organ systems at once.
Chronic Exposure: Skin and Nail Changes
Long-term, low-level arsenic exposure, most commonly through contaminated drinking water, produces a very different picture from acute poisoning. The skin is usually the first place chronic exposure shows up. People develop patches of darkened pigmentation alongside lighter spots, sometimes called a “raindrop” pattern because of its scattered appearance. Thickened, rough skin on the palms and soles of the feet is another hallmark. These changes develop gradually over months to years and are often the reason someone first seeks medical attention.
The fingernails offer another important clue. White horizontal bands called Mees’ lines can appear across the nails roughly two weeks after exposure. These lines run side to side, parallel with the cuticle, usually spanning the full width of the nail. They’re smooth, not ridged, and they don’t fade when you press on them. While Mees’ lines aren’t exclusive to arsenic, their presence alongside other symptoms is a strong signal.
Nerve and Blood Vessel Damage
Chronic arsenic exposure can damage peripheral nerves, causing numbness, tingling, and weakness that typically starts in the hands and feet and moves inward. This pattern resembles other types of nerve damage, which is one reason arsenic poisoning is sometimes misdiagnosed.
Blood vessels take a hit as well. Studies in Taiwan and Chile found that people drinking water with arsenic levels between 0.8 and 1.82 parts per million (normal drinking water contains less than 0.01 ppm) had significantly higher rates of peripheral vascular disease and cardiovascular death. In Taiwan, prolonged exposure to contaminated well water led to gangrene of the extremities, a condition known locally as “blackfoot disease,” with risk increasing alongside both arsenic concentration and age. Workers exposed to arsenic in industrial settings have also developed Raynaud’s disease, a condition where blood vessels in the fingers and toes spasm in response to cold, turning the skin white or blue. High blood pressure has been reported with long-term exposure as well.
Cancer Risk From Long-Term Exposure
Arsenic is a confirmed human carcinogen. The strongest links are with skin, lung, and bladder cancer. Chronic ingestion can also raise the risk of kidney, liver, and prostate cancers, though the evidence for these is less robust. These cancers may not appear until years or even decades after exposure begins, making the connection between cause and effect difficult to trace without testing.
How Arsenic Poisoning Is Detected
Because the symptoms of chronic arsenic exposure overlap with many other conditions, testing is essential for a definitive answer. A 24-hour urine collection is the most common test. Total arsenic levels above 100 micrograms per liter are considered abnormal. Blood testing can also be useful: arsenic levels in blood are normally below 1 microgram per deciliter in people without exposure.
If you’re concerned about your water supply, the current U.S. EPA standard for arsenic in drinking water is 10 parts per billion, a limit set in 2001 to replace the previous, more lenient standard of 50 ppb. Private wells are not regulated under this rule and can be tested through your local health department or a certified lab. Arsenic is colorless and tasteless in water, so testing is the only reliable way to know whether it’s present.
Common Sources of Exposure
Most chronic arsenic exposure worldwide comes from contaminated groundwater, particularly in parts of South and Southeast Asia, Latin America, and some regions of the United States where naturally occurring arsenic leaches into aquifers. Other sources include certain pesticides, pressure-treated wood manufactured before 2004, some traditional or herbal remedies, and occupational exposure in mining, smelting, and semiconductor manufacturing. Rice and rice products can also contain measurable arsenic because the plant absorbs it efficiently from soil and water, though the levels are generally far lower than those associated with poisoning.