Arsenic and the Skin: What Is It? A Dermatologist Explains After the Department of Medical Services Warning
Updated: 2 days ago
Image: Anita Ghosh/REACH · CC BY 2.0 · cropped
Written by นพ. ภัทร วรวุทธินนท์, dermatologist
Arsenic is a metalloid found in nature, especially in groundwater, and also in industrial and mining areas. High-dose or long-term exposure can affect health and the skin, including darkening on the trunk, armpits and groin, a raindrop-like pattern of paler spots, hard bumps on the palms and soles, or white bands across the nails. The latest statement from Thailand's Department of Disease Control (DDC) on 4 November 2026, however, says arsenic levels found in the bodies of people in at-risk groups are still relatively low, and no symptoms have been found. Long-term monitoring is still needed. If your skin changes colour, you develop hard raised bumps, or you have a persistent rash, see a dermatologist.
This article explains the 11 November 2026 warning from the Institute of Dermatology, Department of Medical Services, on how arsenic relates to the skin, which signs to watch for, and where surveillance stands now.
Latest news: what did the Department of Medical Services say about arsenic and the skin?
On 11 November 2026 the Institute of Dermatology, Department of Medical Services, warned the public about arsenic and its effects on the skin, especially for people who live in at-risk areas or may be exposed through the environment or their work. Dr Weerawut Imsamran, Director-General of the Department of Medical Services, said that high-dose or long-term exposure may affect the nervous system, the digestive system, the cardiovascular system and the skin. Thai PBS reported the same warning on the same day.
Earlier, on 4 November 2026, the DDC described health surveillance of at-risk residents in the Kok, Sai, Ruak, Salween and Mekong river basins in 2025–2026. The share of people with relatively high urine arsenic had a rising trend, and total urine arsenic in 2026 was higher than in 2025 in Chiang Rai and Chiang Mai.
An expert meeting on 29 October 2026, however, advised that the amounts detected in the body were still relatively low and were not yet affecting health. The DDC also said that, so far, no clinical signs had been found, but it must still investigate why people in the same at-risk areas have different urine levels, and must follow their health over time. The DDC asked the public to follow the principle: know the risk, do not panic, prevention is possible.
What is arsenic, and how does it enter the body?
Arsenic is a metalloid found in nature, especially in groundwater, and also in industrial and mining areas. The World Health Organization (WHO) notes that inorganic arsenic, such as the form found in water, is highly toxic, while organic arsenic, found mainly in seafood, is less harmful to health.
People may be exposed by drinking or cooking with contaminated water, through related work, or from the environment in at-risk areas. A high dose over a short period often causes nausea, vomiting, abdominal pain and severe diarrhoea. Direct contact may irritate the skin, causing redness or swelling.
Long-term exposure is different. Skin changes from high-level inorganic arsenic usually do not appear in a few days. WHO states that the first signs of long-term high-level exposure are usually seen on the skin — pigmentation changes, skin lesions and hard patches on the palms and soles — after a minimum of about five years, and they may precede skin cancer. Risk is linked to dose and duration, not necessarily a single contact.
Arsenic in the body: what do current test results show?
The test highlighted by the Institute of Dermatology is mainly a urine arsenic level, sometimes with blood, hair or nail testing as appropriate, together with an exposure history and a skin examination.
DDC surveillance in 2025–2026 points to a rising share of people with relatively high urine arsenic in some areas. Experts still judged the amounts found to be relatively low, not yet affecting health, and no symptoms have been found so far. A urine result alone does not mean that someone already has symptomatic arsenic poisoning, and it should not be interpreted from the news without a doctor's assessment.
The DDC is still investigating exposure factors and why results can differ among people in the same at-risk area. This is a surveillance update, not a conclusion that arsenic-related illness has already been identified in these areas.
What does mottled darkening from arsenic look like?
Skin signs that the Institute of Dermatology described after prolonged exposure include darkening, especially on the trunk, armpits and groin. Some people have paler spots within the darkened skin, resembling raindrops on a dusty road.
Image: Khatun et al. · CC BY 4.0 · cropped
This pattern is one clue doctors look for when considering long-term arsenic exposure. Dark or mottled skin has many other causes, such as drug-induced dark marks (in Thai) or melasma from sunlight and hormones, so you should not conclude on your own that arsenic is the cause. A doctor will consider the pattern, the site and the exposure history together.
What are the hard bumps on palms and soles from arsenic?
Prolonged exposure may also cause the skin to thicken into hard, corn-like bumps on the palms and soles, called arsenical keratoses. The Institute of Dermatology notes that some of these lesions may develop into skin cancer, so hard bumps or unusual thickening on the palms or soles should be examined, especially if mottled darkening is also present.
Image: Khatun et al. · CC BY 4.0 · cropped
These bumps are not the same as sun-related rough patches (actinic keratosis) (in Thai), which usually arise on chronically sun-exposed skin. Both should be shown to a dermatologist, because each can be linked to skin-cancer risk in a different way. Do not pick, cut or treat them yourself as if they were ordinary warts.
What are Mees' lines and when do they appear after arsenic exposure?
The Institute of Dermatology states that white bands running across the nails, called Mees' lines, may appear about 8 weeks after arsenic exposure. This finding is not unique to arsenic poisoning and is not, on its own, proof of arsenic in the body. If you are concerned, a doctor should look at the nails together with the skin and the exposure history.
Image: Yannick Trottier · CC BY-SA 3.0
What is Blackfoot disease, and how is it different from a skin rash?
The Institute of Dermatology notes that, in some cases, severe disease of the small blood vessels in the extremities can lead to poor blood supply in the feet, known as Blackfoot disease. This is a serious vascular condition associated with prolonged arsenic exposure in some settings. It is not an ordinary rash or skin bump.
In the DDC's latest surveillance, no symptoms have been found in the people tested, and experts judged the detected levels still relatively low. Mentioning Blackfoot disease is meant to explain a sign that doctors watch for over the long term. It does not mean this condition has been found in Thailand's current surveillance areas.
How does arsenic raise the risk of skin cancer?
Long-term arsenic exposure increases the risk of skin cancer, especially squamous cell carcinoma (SCC) (in Thai) and basal cell carcinoma (BCC) (in Thai), as well as Bowen's disease. The Institute of Dermatology describes Bowen's disease as an early form of skin cancer: a red, brown or skin-coloured patch with scale, which may appear on skin that is not sun-exposed. WHO and the International Agency for Research on Cancer (IARC) classify arsenic and arsenic compounds as carcinogenic to humans, and arsenic in drinking-water as carcinogenic to humans as well.
Risk depends on dose and duration. Not everyone who has been exposed will develop cancer, and current domestic surveillance still describes relatively low levels and no symptoms. If you have a patch, a hard bump or a sore that does not settle, see a dermatologist. A skin biopsy may be needed. Watching for skin-cancer warning signs (in Thai) is also useful, especially if a mark is new or changing.
When should you see a dermatologist?
See a dermatologist if you have
a change in skin colour, especially darkening on the trunk, armpits or groin, or paler spots in a mottled pattern
hard bumps or unusual thickening on the palms or soles
a persistent rash of unknown cause, or a scaly patch that returns
white bands across the nails, together with a history of living or working in an at-risk area
If a lesion might be skin cancer, a biopsy may be needed. Do not wait for it to spread, and do not buy a cream to treat the bumps yourself. People in surveillance areas who notice skin changes are advised by the DDC to see a doctor, and may also call the DDC hotline 1422 or ask local public-health staff.
How can you reduce arsenic risk?
Official advice is consistent: use drinking water from a clean, safe source; do not use water from a contaminated waterway for household consumption; avoid direct contact with arsenic, especially in at-risk areas or related workplaces; and keep watching your skin, nails and general health.
WHO states that, in affected communities, the most important step is a safe water supply for drinking, cooking and irrigating food crops. Follow official updates on testing of water, plants, vegetables and aquatic animals in your area, and the latest local advice.
Frequently asked questions about arsenic and the skin
What is arsenic?
Arsenic is a metalloid found in nature, especially in groundwater, and also in industrial and mining areas. Inorganic arsenic, such as the form in water, is more toxic than organic arsenic, which is found mainly in seafood. A high dose over a short period can cause severe digestive symptoms. Long-term accumulation may affect the skin and other organs.
How is arsenic in the body tested?
A doctor reviews the exposure history, examines the skin, and usually tests the urine arsenic level. Blood, hair or nails may be tested as well, when appropriate. A urine result alone does not mean that symptoms are already present. A doctor should interpret the result together with the skin findings and the history.
What skin symptoms can arsenic cause?
After prolonged exposure, the skin may darken on the trunk, armpits and groin; paler spots may appear within the darkened skin, like raindrops on a dusty road; and hard, corn-like bumps may form on the palms and soles (arsenical keratoses). White bands across the nails (Mees' lines) may appear about 8 weeks after exposure, according to the Institute of Dermatology. These findings have other causes too, so they should be examined by a dermatologist.
How serious is arsenic poisoning, and what do current levels show?
Effects depend on the form, the amount and the duration of exposure. Long-term high-level exposure can raise the risk of skin changes and some cancers. The DDC statement of 4 November 2026, however, said that amounts found in at-risk groups were still relatively low, were not yet affecting health, and that no symptoms had been found so far. Continue prevention and monitoring, without panic.
What is a raindrops-on-a-dusty-road pattern?
It is darkened skin with paler spots scattered through it, resembling raindrops on dusty ground. The Institute of Dermatology says this may be seen after long-term arsenic exposure, often together with darkening of the trunk, armpits or groin. The pattern is not always specific enough to diagnose by eye alone. See a dermatologist if you are concerned.
What are Mees' lines, and how many weeks after arsenic exposure do they appear?
Mees' lines are white bands running across the nails. The Institute of Dermatology states that they may appear about 8 weeks after arsenic exposure. Similar bands can also have other causes, including some medicines. Do not conclude on your own that they mean arsenic poisoning; a doctor should assess the nails together with the skin and the exposure history.
Can arsenic cause skin cancer?
Long-term exposure increases the risk of SCC and BCC, as well as Bowen's disease, an early skin cancer that may appear on skin that is not sun-exposed. This does not mean everyone who has been exposed will develop cancer. Risk depends on dose and duration. Current surveillance in at-risk groups still describes relatively low levels and no symptoms. A persistent patch, hard bump or chronic rash should be examined.
What should I do if I live in a surveillance area?
Know the risk, do not panic, and focus on prevention. Use drinking water from a clean, safe source, do not use water from a contaminated waterway for household consumption, avoid direct contact with arsenic, and watch your skin. If the colour changes, hard bumps appear, or a rash persists, see a doctor. You can also ask local public-health staff or call the DDC hotline 1422.
See a dermatologist at คลินิกเฉพาะทางผิวหนัง Siam Dermatology
If your skin has changed colour, you have hard raised bumps, a persistent rash or white bands across the nails, and you would like a dermatologist to assess them, you can book an examination at คลินิกเฉพาะทางผิวหนัง Siam Dermatology. The doctor will take a history, examine the skin and consider further tests as appropriate. More details: general dermatology services (in Thai) and mole and skin-cancer checks (in Thai)
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