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

October 6, 2025 •

4 min read

While selenium is a vital trace mineral, consuming amounts above the 400 mcg daily Tolerable Upper Intake Level can lead to toxicity. Selenosis, or selenium toxicity, can cause a range of symptoms from mild discomfort to severe health complications. Understanding what are the symptoms of too much selenium in the body is crucial for anyone taking supplements or consuming large quantities of high-selenium foods.

Quick Summary

Overconsumption of the trace mineral selenium can result in selenosis, causing symptoms such as hair loss, brittle nails, skin rashes, fatigue, gastrointestinal upset, and a distinct garlic-like breath odor.

Key Points

Garlic Breath: A distinctive, garlic-like odor on the breath is a hallmark sign of selenium excess, caused by the body's metabolism of the mineral.
Hair and Nail Changes: Chronic selenosis often manifests as hair loss (alopecia) and brittle, discolored nails that can eventually shed.
Gastrointestinal Distress: Early and common symptoms include nausea, vomiting, diarrhea, and stomach pain, which can be mistaken for other conditions.
Neurological Issues: Excessive selenium can cause peripheral neuropathy, characterized by tingling sensations, along with fatigue and irritability.
Causes of Overdose: The most common causes are excessive supplementation and consuming too many Brazil nuts, which are exceptionally high in selenium.
Prevention is Key: To prevent toxicity, avoid exceeding the Tolerable Upper Intake Level of 400 mcg per day and monitor your total intake from both food and supplements.

Recognizing the Dangers of Selenosis

Selenium is a powerful antioxidant that plays an essential role in thyroid hormone metabolism, DNA synthesis, and protecting the body from oxidative damage. However, the line between an adequate intake and a toxic one is surprisingly narrow. The primary cause of selenium toxicity (selenosis) is the long-term, excessive use of dietary supplements, often in dosages far exceeding the recommended daily allowance of 55 micrograms for adults. Accidental over-ingestion of misformulated supplements has also led to widespread outbreaks of acute toxicity. Another, more subtle risk comes from regularly eating foods with very high concentrations of selenium, most notably Brazil nuts.

Acute vs. Chronic Selenium Toxicity

Selenium toxicity can manifest in two forms, depending on the exposure level and duration.

Acute toxicity occurs from a single, massive overdose of selenium. This can happen with accidental ingestion of industrial compounds or severely mislabeled supplements. The symptoms are typically severe and rapid, potentially including extreme gastrointestinal distress, neurological problems, and in rare, severe cases, organ failure and death.
Chronic toxicity results from consistently consuming lower doses of excess selenium over an extended period. The onset of symptoms is more gradual, and the effects are cumulative. Chronic selenosis is more common than acute poisoning and is primarily associated with issues affecting the hair, nails, and skin.

Common Symptoms of Too Much Selenium

Excessive selenium intake leads to a constellation of distinct symptoms, though not everyone will experience all of them. The presentation can vary depending on the severity and duration of the overdose.

Gastrointestinal Upset

Many of the initial symptoms are digestive in nature, which can be easily mistaken for other illnesses.

Nausea and vomiting
Diarrhea
Abdominal pain

Hair and Nail Problems

Some of the most characteristic signs of chronic selenosis involve changes to the hair and nails.

Hair Loss: Known medically as alopecia, this can range from noticeable thinning to severe, patchy hair loss. Excessive selenium disrupts the hair growth cycle, causing follicles to prematurely enter the resting phase.
Brittle and Discolored Nails: Nails can become fragile, discolored, and show white horizontal streaks. In more advanced cases, the nails may shed entirely.

Neurological and Systemic Effects

Selenosis also impacts the nervous system and overall bodily functions.

Fatigue and Irritability: Unexplained and persistent tiredness and mood changes are common complaints.
Peripheral Neuropathy: This can cause tingling sensations in the extremities, often described as “pins and needles”.
Muscle Tenderness: Unexplained muscle aches and weakness can develop.

A Distinctive Odor

One of the most unique and telling symptoms of selenium excess is a strong, unpleasant breath odor.

Garlic-like breath odor: Excess selenium is metabolized into dimethyl selenide, which is excreted through the lungs and sweat glands, causing a garlic-like smell.
Metallic Taste: A metallic or garlicky taste in the mouth is also frequently reported.

Comparison of Acute and Chronic Selenosis Symptoms


Symptom	Acute Selenosis	Chronic Selenosis (Selenosis)
Gastrointestinal	Severe nausea, vomiting, diarrhea, abdominal pain	Milder nausea and diarrhea, but persistent
Hair & Nails	Rapid and widespread hair loss and nail changes	Progressive hair thinning, brittle nails with streaks
Neurological	Tremors, confusion, ataxia (impaired coordination)	Paresthesias (tingling), hyperreflexia, fatigue
Cardiovascular	Can lead to severe cardiac problems, heart failure	Generally not a feature, though can affect cholesterol long-term
Breath/Taste	Distinctive, strong garlic-like odor	Persistent garlic-like breath odor and metallic taste
Skin	Acute skin rashes	Dermatitis, skin lesions

Management and Prevention of Selenium Toxicity

If selenosis is suspected, the first and most critical step is to stop all sources of excessive selenium intake immediately. This includes halting supplementation and re-evaluating the intake of high-selenium foods like Brazil nuts. Consulting a healthcare provider is essential for proper diagnosis and monitoring. Blood and urine tests can help confirm elevated selenium levels.

Management focuses on supportive care and removal of the excess mineral source. The body will naturally excrete the excess selenium over time, but recovery can be a slow process. Depending on the severity of the toxicity, it may take several months for symptoms to subside and for hair and nail growth to normalize. In some severe cases, permanent damage to hair follicles may occur.

Prevention is the most effective approach. The Tolerable Upper Intake Level (UL) for selenium is 400 micrograms (mcg) per day for adults, and this should not be exceeded without medical supervision. Always read supplement labels carefully, especially multivitamin and hair/nail support products, as their combined selenium content can push daily intake over the limit. Furthermore, be mindful of high-selenium foods; for instance, a single Brazil nut can contain up to 91 mcg of selenium.

Conclusion: Moderation is Key for this Essential Mineral

In conclusion, while selenium is indispensable for good health, the risks of overconsumption are significant and can lead to a condition known as selenosis. The symptoms, which include hair loss, brittle nails, a garlic-like breath odor, gastrointestinal upset, fatigue, and neurological issues, highlight the importance of careful moderation. The easiest way to avoid toxicity is to be mindful of supplement intake and not to exceed the recommended Tolerable Upper Intake Level of 400 mcg daily. By understanding what are the symptoms of too much selenium in the body and staying vigilant about dietary sources and supplements, individuals can reap the benefits of this essential mineral without risking harmful side effects.

For more detailed information on dietary supplements and nutrient intake, consult the National Institutes of Health (NIH) Office of Dietary Supplements website.

Frequently Asked Questions

For adults, the Tolerable Upper Intake Level (UL) for selenium is 400 micrograms (mcg) per day. Exceeding this amount, especially over a prolonged period, increases the risk of selenium toxicity, or selenosis.

While it is rare, it is possible to consume too much selenium from food alone, particularly if you eat large quantities of Brazil nuts. A single Brazil nut can contain a very high amount of selenium, and eating multiple nuts daily could push your intake over the safe limit.

The primary treatment for selenium toxicity is to stop all sources of excessive selenium intake immediately. Management is largely supportive, focusing on symptom relief while the body naturally excretes the mineral. A healthcare provider can confirm elevated levels through blood or urine tests.

Recovery time depends on the severity and duration of the toxicity. After stopping the excess intake, it can take several weeks to months for selenium levels to normalize. Full recovery of symptoms like hair and nail growth may take up to a year.

When the body has too much selenium, it metabolizes the excess into dimethyl selenide. This compound is excreted through the lungs and sweat glands, producing a distinct and characteristic garlic-like odor on the breath.

In most cases, symptoms of mild to moderate selenosis are reversible once intake is reduced. However, severe or prolonged toxicity can potentially cause permanent damage, including damage to hair follicles.

A healthcare provider can order a blood or urinary test to measure your selenium levels. This is typically done if selenosis is suspected based on your symptoms and a history of high intake, such as from supplements.

Yes, if you take multiple supplements that contain selenium, you could unknowingly exceed the Tolerable Upper Intake Level. Always check the labels of all supplements you take to calculate your total daily intake.