What are the symptoms of excess selenium?

November 22, 2025 •

3 min read

While selenium is a crucial trace mineral, with the recommended daily intake for adults being 55 micrograms, exceeding the safe upper limit of 400 micrograms can cause toxicity. Understanding what are the symptoms of excess selenium is vital, as this condition, known as selenosis, can lead to a variety of adverse health effects affecting the skin, nails, hair, and nervous system.

Quick Summary

Excess selenium, known as selenosis, results from high intake, often from supplements or certain foods. Common signs include hair loss, brittle nails, a garlic-like breath odor, gastrointestinal upset, and fatigue. Severe cases can lead to serious neurological and systemic problems.

Key Points

Hair and Nail Changes: Excess selenium causes hair loss (alopecia) and makes nails brittle, discolored, or prone to shedding.
Garlic Breath: A distinctive, garlic-like odor on the breath is a classic symptom of selenosis due to the body's metabolic processing of the mineral.
Gastrointestinal Distress: Nausea, vomiting, and diarrhea are common symptoms of selenium toxicity, particularly in acute cases.
Neurological Issues: Long-term, high exposure can lead to nerve damage, causing tingling, numbness, and fatigue.
Acute vs. Chronic Toxicity: Symptoms differ based on the type of exposure; chronic exposure causes gradual hair/nail damage, while acute poisoning can be a medical emergency.
Supplementation Risk: Over-the-counter supplements are a frequent cause of excess selenium, especially when misformulated or taken in high doses.
Balance is Key: Maintaining a balanced intake through diet is the safest way to get adequate selenium, as the mineral is essential but toxic in high doses.

Understanding Selenosis: The Dangers of Too Much Selenium

Selenium is a powerful antioxidant essential for numerous bodily functions, including thyroid health and immune system regulation. However, the line between an optimal intake and a toxic one is surprisingly thin, especially when relying on supplements or high-selenium foods like Brazil nuts. When the body's selenium levels become excessive, it leads to a condition called selenosis, which manifests through a distinctive set of symptoms. Awareness of these warning signs is crucial for preventing more severe health complications.

Hair and Nail Abnormalities

One of the most noticeable and common signs of chronic selenium toxicity is its effect on hair and nails. As the body accumulates excess selenium, a clear pattern of damage emerges.

Hair Loss (Alopecia): Selenosis frequently causes significant hair loss, which can affect the entire body, not just the scalp. The hair often becomes brittle and breaks easily.
Brittle and Discolored Nails: Nails can become discolored, brittle, or develop white, horizontal streaks (transverse lines). In more severe cases, the nails may even be shed entirely.

Gastrointestinal and Nervous System Disturbances

Excess selenium doesn't just affect external features; it can wreak havoc on internal systems as well. The gastrointestinal tract is often one of the first areas to show symptoms.

Nausea and Diarrhea: These are among the main gastrointestinal symptoms associated with selenium toxicity.
Metallic Taste and Garlic Breath: A strong, garlic-like odor on the breath is a hallmark sign of excess selenium, caused by the body's processing of the mineral. Patients may also experience a distinct metallic taste in their mouth.
Fatigue and Irritability: General fatigue, lethargy, and increased irritability are common systemic effects reported in those with selenosis.
Peripheral Neuropathy: More serious cases of toxicity can lead to nerve damage, resulting in symptoms like numbness, tingling sensations (paresthesia), and pain in the extremities.

Differentiating Acute vs. Chronic Selenosis

Selenium toxicity can be either acute (short-term, high-dose exposure) or chronic (long-term, moderate-to-high dose exposure). The presentation of symptoms can vary depending on the nature of the exposure.


Feature	Chronic Selenosis	Acute Selenosis
Cause	Prolonged, excessive intake from supplements or diet.	High-dose, short-term ingestion, often due to a misformulated supplement or accidental overdose.
Symptom Onset	Gradual, with symptoms like hair loss and brittle nails developing over weeks to months.	Rapid, with severe symptoms appearing within hours to days of ingestion.
Key Symptoms	Hair loss, brittle nails, garlic breath, fatigue, GI upset, irritability.	Severe gastrointestinal distress, neurological symptoms, respiratory distress, kidney and heart failure.
Severity	Generally less severe, but can still cause significant and lasting damage.	Can be life-threatening, potentially leading to death in rare cases.

The Importance of Balanced Intake

While this article focuses on the risks of excess selenium, it's important to remember that this is still a rare condition compared to deficiency. The key to reaping the benefits of selenium is to maintain a balanced intake, typically through diet. Consuming a variety of foods such as seafood, lean meats, and whole grains should provide sufficient amounts for most people. Regular consumption of extremely high-selenium foods, like Brazil nuts, or using high-dose supplements without medical supervision carries a higher risk. The National Institutes of Health (NIH) provides extensive resources on safe intake levels and potential health effects.

Conclusion

Recognizing what are the symptoms of excess selenium is critical for anyone taking supplements or consuming high-selenium foods. The signs, ranging from cosmetic changes like hair and nail problems to more severe neurological and gastrointestinal issues, provide important clues to a potentially dangerous overconsumption. If you suspect selenosis, discontinuing the selenium source is the primary step, followed by immediate medical consultation to prevent long-term damage. A balanced diet remains the safest and most effective way to ensure adequate selenium intake without risking toxicity.

Frequently Asked Questions

The most common cause of excess selenium, known as selenosis, is the overconsumption of dietary supplements. Eating extremely high-selenium foods, such as Brazil nuts, in large quantities can also contribute.

The tolerable upper intake level for adults is 400 micrograms per day. Consistently exceeding this amount, particularly through supplements, can increase the risk of toxicity.

It is difficult but not impossible to develop selenosis from diet alone. It would require regular, excessive consumption of high-selenium foods, like eating a large number of Brazil nuts daily.

Early symptoms often include a garlic odor on the breath and a metallic taste in the mouth. Fatigue and mild gastrointestinal issues can also appear gradually.

In rare cases, acute selenium toxicity from a massive, single overdose can be fatal. This is typically from misformulated supplements or accidental ingestion of large amounts.

Diagnosis is typically based on a patient's history of high selenium intake and a physical examination of symptoms. Blood or urine tests can be used to measure selenium levels.

Treatment involves discontinuing the source of high selenium intake. For acute poisoning, supportive medical care is necessary. Symptoms often resolve after reducing intake, but some effects, like nail damage, may take longer to heal.