What are the symptoms of selenium toxicity? Understanding selenosis and its effects

January 5, 2026 •

3 min read

In 2008, an outbreak of acute selenium poisoning was caused by a misformulated liquid dietary supplement containing 200 times the labeled amount of selenium, affecting over 200 people with severe adverse reactions. This incident highlights the critical importance of understanding what the symptoms of selenium toxicity are and the dangers of excessive intake.

Quick Summary

Selenosis, or selenium toxicity, can cause a range of issues from chronic problems like hair and nail loss to acute, life-threatening conditions involving severe organ damage. Signs often include a distinct garlic odor on the breath, fatigue, gastrointestinal distress, and neurological effects.

Key Points

Garlic Breath: A distinct, garlic-like odor on the breath is a hallmark sign of selenium toxicity due to the body's excretion of volatile selenium compounds.
Hair and Nail Damage: Excess selenium can cause hair loss, brittle or discolored nails, and in severe cases, the shedding of nails.
Gastrointestinal Issues: Mild toxicity often presents with gastrointestinal symptoms such as nausea, diarrhea, and general stomach upset.
Neurological Symptoms: Selenosis can affect the nervous system, leading to fatigue, irritability, and peripheral neuropathy, which is characterized by tingling in the extremities.
Acute vs. Chronic: Symptoms vary based on exposure; chronic exposure causes gradual signs, while acute overdose from supplements can cause severe, life-threatening organ damage.
Source of Toxicity: Over-supplementation is the most common cause, but regular, high consumption of selenium-rich foods like Brazil nuts and environmental exposure can also lead to toxicity.

What is Selenium Toxicity?

Selenium is an essential trace mineral vital for many bodily functions, including antioxidant protection and thyroid hormone metabolism. However, there is a narrow margin between beneficial and toxic levels. Excessive intake, frequently from high-dose dietary supplements, leads to selenium toxicity, medically termed selenosis. Symptoms can vary significantly based on whether exposure is chronic (long-term) or acute (sudden and severe).

Common Chronic Symptoms

Chronic selenium toxicity results from consistent consumption of amounts slightly above the tolerable level over time. The Tolerable Upper Intake Level (UL) for adults is 400 micrograms (mcg) per day. Chronic selenosis symptoms typically develop gradually and affect the hair, nails, and nervous system.

Garlic Breath Odor: A distinct, garlic-like or metallic smell on the breath is a classic indicator of selenium toxicity, resulting from the body's excretion of excess selenium compounds.
Hair and Nail Changes: Common manifestations include hair loss (alopecia) and brittleness. Nails may become brittle, discolored, deformed, or shed entirely in severe cases.
Gastrointestinal Issues: Symptoms like nausea, diarrhea, and abdominal discomfort are frequently reported.
Fatigue and Weakness: General tiredness is a persistent complaint among individuals with selenosis.
Neurological Effects: Mild neurological issues can arise, such as fatigue, irritability, and peripheral neuropathy, which may cause tingling in the extremities.

Severe Acute Symptoms

Acute selenium toxicity is a medical emergency that can occur after ingesting a large dose of selenium, often from improperly formulated supplements. Severe symptoms can include organ failure and myocardial infarction. There may also be severe neurological distress, flushing, and other effects.

Table: Comparison of Chronic vs. Acute Selenium Toxicity Symptoms


Symptom	Chronic Selenosis	Acute Selenosis
Onset	Gradual, over weeks or months	Sudden and severe, within hours or days
Hair	Loss and brittleness	Rapid, severe hair loss
Nails	Brittleness, discoloration, shedding	Discoloration, brittleness, and loss
Breath	Persistent garlic odor	Often includes strong garlic odor
Gastrointestinal	Nausea, diarrhea, stomach upset	Severe gastrointestinal issues, vomiting
Neurological	Peripheral neuropathy, fatigue, irritability	Tremors, irritability, myalgia, potential paralysis
Cardiovascular	Possible links to heart issues at lower doses	Myocardial infarction, cardiac failure
Severity	Ranges from mild to severe, but typically not immediately fatal	Medical emergency, can be fatal

Causes of High Selenium Intake

While adequate selenium is typically obtained from the diet, excessive intake can result from dietary supplements (the most common cause), high-selenium foods like Brazil nuts, and environmental or occupational exposure. Brazil nuts can contain a high amount of selenium per nut.

What to Do If You Suspect Selenium Toxicity

If you experience any of these symptoms, it is crucial to consult a healthcare provider. Diagnosis involves reviewing intake and potentially ordering tests to measure selenium levels. The primary treatment is to eliminate the source of excessive selenium.

Steps for Managing and Treating Selenosis:

Stop Supplements: Immediately discontinue selenium-containing supplements.
Adjust Diet: Avoid high-selenium foods such as Brazil nuts and certain seafood until levels normalize.
Supportive Care: Mild cases usually resolve with supportive care, while more severe cases may require medical management of symptoms.
Medical Intervention: In rare cases of severe acute poisoning, medical therapies may be considered, although there is no specific antidote.

Conclusion

Selenium is an essential nutrient, but excessive intake, especially from supplements, can cause significant health problems. Symptoms of selenium toxicity (selenosis) range from common issues like hair and nail changes to severe, life-threatening complications. Prevention relies on moderation, adhering to recommended intake levels, and consulting a healthcare provider before taking high-dose supplements. Recognizing the signs and taking prompt action is vital for mitigating the health risks of selenosis.

For more detailed information on selenium, visit the {Link: NIH Office of Dietary Supplements https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/}.

Frequently Asked Questions

The most common cause of selenium toxicity is the overuse of dietary supplements, especially high-dose products. Other causes include consuming large amounts of certain high-selenium foods and environmental or occupational exposure.

Yes, eating too many Brazil nuts regularly can cause selenium toxicity. Brazil nuts are one of the densest food sources of selenium, and consuming them frequently can easily push daily intake above safe levels.

A distinct garlic-like odor on the breath is a characteristic symptom of selenosis, but it is not the only one. It is caused by the body metabolizing and excreting excess selenium, but should be considered alongside other symptoms and medical evaluation.

Diagnosis typically involves a physical examination and an assessment of the patient's diet and supplement history. Blood or urinary tests can be conducted to measure selenium levels and confirm excessive intake.

The primary treatment is to remove the source of the excess selenium, such as discontinuing supplements or adjusting the diet. Treatment is mostly supportive, focusing on symptom management. There is no specific antidote.

Recovery from mild to moderate selenosis usually occurs within weeks to months after removing the source of excess selenium. However, severe acute cases can cause permanent organ damage.

The recommended dietary allowance (RDA) for adult men and women is 55 micrograms (mcg) per day. The Tolerable Upper Intake Level (UL) is 400 mcg per day for adults.