What are the side effects of Selenium?

Potential side effects include: Hair loss at excessive doses (selenosis), Brittle nails, Garlic-like breath odor at high doses, Nausea and diarrhea.

Does selenium support hair health?

Selenium is a trace mineral involved in antioxidant defense and thyroid hormone metabolism, both of which may influence hair growth. Research suggests that both selenium deficiency and excess can contribute to hair loss. A 2016 review in Dermatology Practical & Conceptual noted that selenium plays a role in hair follicle morphogenesis. Supplementation should only be considered when deficiency is confirmed, as excess selenium is toxic.

How much selenium is safe for hair support?

The recommended dietary allowance for selenium is 55 mcg per day for adults, with an upper tolerable limit of 400 mcg. Exceeding this can cause selenosis, which paradoxically includes hair loss as a symptom. Brazil nuts are one of the richest food sources — a single nut may contain 70-90 mcg. Supplementation beyond dietary intake requires professional guidance.

Can selenium supplements cause hair loss?

Yes — excessive selenium intake is a well-documented cause of hair loss (selenosis). The therapeutic window for selenium is narrow: the recommended daily intake is 55 mcg, while toxicity can begin at chronic intakes above 400 mcg per day. Paradoxically, selenium deficiency may also impair thyroid function, which can indirectly affect hair. The Grade F evidence across 35 studies with 10,466 participants indicates selenium supplementation does not improve hair loss at population level.

Why does selenium have negative evidence for hair loss on HairCited?

Selenium receives a Grade F (Negative) rating across 35 studies with 10,466 participants for both thyroid-related and nutritional deficiency hair loss. This means fewer than 30% of studies show positive effects. While selenium is essential for thyroid health — and thyroid dysfunction can cause hair loss — supplementing selenium in populations without confirmed deficiency has not demonstrated measurable benefit for hair outcomes in clinical research.

Is selenium deficiency a common cause of hair loss?

Selenium deficiency is relatively uncommon in developed countries where selenium-rich foods (Brazil nuts, seafood, poultry) are available. It can occur with very restricted diets, malabsorption conditions, or in selenium-poor geographic regions. While severe deficiency may contribute to thyroid dysfunction and subsequent hair loss, the large body of research (35 studies, 10,466 participants) does not support routine selenium supplementation for hair health absent confirmed deficiency.

Selenium

mineral

Also known as: Selenomethionine, Sodium selenite

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About

Selenium is a trace mineral incorporated into selenoproteins that protect hair follicle cells from oxidative damage. It is also essential for thyroid hormone metabolism, which directly influences the hair growth cycle. Both deficiency and excess can cause hair loss.

How It Works

Selenoproteins protect hair follicle cells from oxidative damage; essential for thyroid hormone metabolism.

Evidence For Conditions

Condition	Grade	Studies	Participants
Thyroid-Related Hair Loss	A	38	10748	View →
Nutritional Deficiency Hair Loss	A	38	10748	View →

Side Effects

Hair loss at excessive doses (selenosis)
Brittle nails
Garlic-like breath odor at high doses
Nausea and diarrhea

Drug & Supplement Interactions

Statins (selenium may reduce statin effectiveness)
Chemotherapy drugs (antioxidant effects may theoretically interfere)
Niacin (may decrease HDL-raising effect when combined)

Always inform your healthcare provider about all supplements you take.

Related Ingredients

Iron Silica (Silicon) Zinc

Quick Facts

Dosage: General: 55 mcg/day
Forms: capsule tablet
Natural Sources: Brazil nuts, Tuna, Turkey, Cottage cheese, Brown rice
Upper Limit: 400 mcg/day
Best Time: With meals for better absorption

Evidence Summary

Thyroid-Related Hair Loss A

Nutritional Deficiency Hair Loss A

FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. The products and information on this website are not intended to diagnose, treat, cure, or prevent any disease. The evidence grades presented are based on our analysis of published peer-reviewed research and do not constitute medical advice. Always consult your healthcare provider before starting any supplement regimen.