Nutrition Diet: What are the symptoms of too much selenium?

November 2, 2025 •

3 min read

The tolerable upper intake level for selenium is 400 micrograms per day for adults, according to the NIH Office of Dietary Supplements. Exceeding this limit, often via supplements or specific foods, can lead to a condition known as selenosis. Understanding what are the symptoms of too much selenium? is vital for preventing potentially serious health issues.

Quick Summary

An overdose of selenium, known as selenosis, can cause symptoms such as hair loss, brittle nails, gastrointestinal distress, fatigue, and a characteristic garlic breath odor. Excessive intake is most often due to supplements or overconsumption of Brazil nuts.

Key Points

Hair and Nail Changes: A classic sign of too much selenium is hair loss, along with brittle, discolored, or shedding nails.
Gastrointestinal Distress: Excess selenium commonly causes digestive issues like nausea, vomiting, and diarrhea.
Garlic Breath: A distinctive and tell-tale sign of selenium toxicity is a garlic-like odor on the breath.
Neurological Problems: Overdose can lead to fatigue, irritability, and nerve damage, including tremors and numbness.
Main Causes: Selenosis is most often caused by excessive intake from high-dose supplements or overconsumption of Brazil nuts, rather than from a standard diet.
Severity: While mild cases may resolve by reducing intake, severe toxicity can lead to serious complications, including organ failure.
Reversible Symptoms: In most cases, symptoms improve once excessive selenium intake is stopped, though recovery can take several months.

Selenium is an essential trace mineral that plays a crucial role in the body. It functions as a powerful antioxidant, supports proper thyroid gland function, and contributes to a healthy immune system. While a deficiency can lead to health problems, the line between beneficial and toxic intake is narrow, making excessive consumption a significant risk.

Understanding the Dangers of Selenosis

Selenium toxicity, or selenosis, is a condition caused by the excessive consumption of selenium. The most common cause is the misuse of dietary supplements, with some incidents linked to misformulated products containing dangerously high levels of selenium. Additionally, overconsuming certain selenium-rich foods, particularly Brazil nuts, which have a very high and variable selenium content, can lead to an overdose.

Physical and Dermatological Symptoms

Changes in hair and nails

One of the most noticeable and well-documented symptoms of selenosis is its effect on hair and nails. A high level of selenium can lead to:

Hair loss (alopecia): Hair may become brittle, weak, and eventually fall out in noticeable patches or over the entire scalp.
Brittle nails: Nails become fragile, discolored, or deformed, and may develop white streaks or eventually be shed entirely.

Skin problems

Excessive selenium can also cause various skin issues, including:

Skin rashes and lesions.
Flushing of the skin, which can occur during acute toxicity.

Gastrointestinal and Sensory Disturbances

An overdose of selenium often manifests as significant gastrointestinal distress and peculiar sensory effects.

Garlic breath: A unique and characteristic symptom of selenium toxicity is the breath having a distinct garlic odor, caused by the body's metabolism of selenium.
Metallic taste in the mouth: Patients may report a metallic or bitter taste.
Nausea, vomiting, and diarrhea: These are some of the most common early signs of both chronic and acute selenium excess.

Neurological and Systemic Effects

As selenium levels continue to rise, the central nervous system can be affected, leading to a range of symptoms.

Fatigue and extreme tiredness.
Irritability.
Nervous system problems: This can include dizziness, tremors, and a tingling or prickling sensation in the extremities, a condition known as peripheral neuropathy.
Muscle tenderness.

Comparison of Selenium Deficiency vs. Toxicity Symptoms


Symptom Category	Selenium Deficiency (Rare)	Selenium Toxicity (Selenosis)
Hair and Nails	Slower hair growth, hair shedding.	Brittle nails, nail discoloration, and severe hair loss.
Thyroid Function	Thyroid issues, such as autoimmune thyroiditis.	Can potentially harm thyroid function at high doses.
Heart Health	Increased risk of heart disease (e.g., Keshan disease).	Potential for heart problems, and in severe cases, heart failure.
Neurological	Fatigue, mental fog, lethargy, confusion.	Irritability, nerve damage (peripheral neuropathy), tremors.
Gastrointestinal	Not typically a primary symptom.	Nausea, vomiting, diarrhea, and abdominal pain.
Other Indicators	May show signs of weakened immune response.	Garlic breath, metallic taste in mouth, skin rashes.

Severe and Long-Term Health Risks

While mild to moderate selenosis symptoms typically resolve after reducing intake, severe cases can lead to more critical health complications. These include:

Kidney or heart failure.
Acute respiratory distress syndrome (ARDS).
Cirrhosis.
In rare and extreme instances, acute toxicity can be fatal.

Diagnosis and Treatment for Excessive Selenium

If selenium toxicity is suspected, it is crucial to consult a healthcare provider. Diagnosis is based on a patient's history of high selenium intake, evaluation of physical symptoms, and confirmation through laboratory tests.

Testing: Blood or urinary selenium levels can be measured to confirm an overdose.
Treatment: There is no specific antidote for selenium poisoning. The primary treatment is to immediately stop all selenium supplements and reduce intake from dietary sources. Supportive care is administered to manage symptoms.
Recovery: Most symptoms, like hair loss and nail deformities, are reversible over time once intake is normalized. It may take months for the body's levels to return to normal and for symptoms to resolve.

Conclusion: The Importance of Moderation

Selenium is a vital nutrient for overall health, but the risks associated with overconsumption are significant. The most effective way to prevent selenosis is to obtain selenium from a balanced diet rather than relying on high-dose supplements. The average adult should not exceed the 400 mcg daily upper limit. Always consult a healthcare professional before starting any new supplement regimen, as many common supplements contain selenium, and it is easy to inadvertently exceed the safe limit.

For more detailed information on selenium intake and health, refer to the NIH Office of Dietary Supplements.

Frequently Asked Questions

Hair loss typically occurs when selenium intake regularly exceeds the tolerable upper intake level of 400 micrograms (mcg) per day for adults. High-dose supplements or consuming too many Brazil nuts are common causes.

Symptoms can vary depending on the dosage and duration. Chronic, long-term overexposure can cause symptoms to appear over weeks or months, while acute, very high intake can lead to rapid onset of severe symptoms.

The main treatment for selenium toxicity is to discontinue all sources of excessive selenium intake, including supplements and high-selenium foods. Treatment then focuses on supportive care to manage symptoms.

While most symptoms of mild to moderate selenosis are reversible upon reducing intake, severe or prolonged toxicity can potentially lead to permanent damage, particularly to hair follicles, nerves, or internal organs.

The most definitive way to know is through a blood or urine test to measure selenium levels. However, common warning signs include hair and nail problems, gastrointestinal issues, fatigue, and a garlic-like breath odor.

Brazil nuts are the most concentrated source of selenium. Other food sources include seafood, lean meats, poultry, eggs, and some grains, though the selenium content can vary based on soil levels.

It is difficult to get a toxic dose of selenium from a balanced diet alone. The main risk comes from over-supplementation or regular consumption of large quantities of very high-selenium foods, such as Brazil nuts.