Quick answer

Yes, too much selenium over time can. NIH names hair loss and brittle or lost nails as the most common signs of selenosis, and EFSA based its 255 mcg upper limit on hair loss seen at 330 mcg a day. Ask your doctor if your hair is thinning while you take selenium.^1,2,3

Key facts

NIH calls hair loss and brittle or lost nails the most common signs of long-term high selenium intake.¹
The US upper limit of 400 mcg a day was set from amounts linked with hair and nail brittleness and loss.¹
EFSA's 2023 opinion put its upper limit at 255 mcg a day, using hair loss seen at 330 mcg a day in a large trial.³
In 2008, 201 people had severe reactions to a liquid supplement that held 200 times the selenium on its label.¹
Brazil nuts hold 68 to 91 mcg of selenium each, and many multivitamins list 55 mcg.^1,2

What does NIH say about selenium and hair loss?

Getting too much selenium over time (selenosis) can cause garlic breath, a metallic taste in the mouth, hair loss, brittle nails or nail loss, skin rash, nausea, diarrhea, extreme tiredness, irritability and nervous system problems.^1,2

Garlic breath and a metallic taste are the earliest signs of too much selenium; hair loss and brittle or lost nails are the most common.¹

NIH adds that chronically high intakes of the organic and inorganic forms of selenium have similar effects, so the form on the label does not change the concern.¹

How much selenium has caused hair loss?

The US upper limit for adults is 400 mcg a day from food, drinks and supplements together. NIH says it was set from the amounts associated with hair and nail brittleness and loss, and that it does not apply to people taking selenium under a doctor's care.¹

In 2023 the European Food Safety Authority set a lower upper limit than the United States: 255 mcg a day for adults, including during pregnancy and breastfeeding, based on hair loss.^1,4

EFSA's opinion identified hair loss as an early, well-established effect of excess selenium. It took 330 mcg a day, the amount linked to hair loss in the large SELECT trial, applied a safety factor of 1.3, and arrived at 255 mcg a day. EFSA says adults are unlikely to pass that figure unless they regularly take high-dose supplements or eat Brazil nuts.³

Which products have caused trouble?

In 2008, 201 people had severe reactions to a liquid dietary supplement that contained 200 times the amount of selenium on its label.¹

Very high amounts can cause severe stomach and nervous system problems, difficulty breathing, tremors, lightheadedness, flushing, muscle tenderness, kidney or heart failure, heart attacks and, in rare cases, death.^1,2

Brazil nuts are a food source to count. NIH says they contain 68 to 91 mcg of selenium per nut and could lead to toxicity if eaten regularly.¹

Many multivitamins list 55 mcg of selenium, products that pair selenium with vitamin E or a few other ingredients usually have 50 to 200 mcg, and selenium-only supplements usually have 100 to 400 mcg. Added together with nuts and a multivitamin, they can pass the limit.¹

Does selenium sulfide shampoo cause hair loss?

The over-the-counter dandruff shampoo label read for this page does not list hair loss. It says the product is for external use only and tells people to stop use and ask a doctor if the condition worsens or does not clear up. NIH's selenium fact sheets cover the nutrient, not selenium sulfide, so the sources checked do not settle the question for shampoo.⁵

Who should ask a doctor about selenium and hair loss?

Anyone whose hair is thinning or whose nails are breaking while taking selenium, whether alone, in a multivitamin or with nuts.¹
Anyone who also notices garlic breath or a metallic taste, which NIH calls early signs of too much.¹
Anyone taking a liquid or high-dose selenium product, since mislabeled amounts have caused severe reactions.¹

Many things besides selenium can thin hair, so ask your doctor rather than assuming the cause. Bring the label of every product that lists selenium.

Questions people ask

How much selenium causes hair loss?

EFSA found hair loss at 330 mcg a day in a large trial and set 255 mcg a day as its upper limit. NIH's US limit is 400 mcg a day. Both count all sources together.^1,3

What are the first signs of too much selenium?

NIH says garlic breath and a metallic taste in the mouth are the earliest signs, and hair loss and brittle or lost nails are the most common. Ask your doctor if you notice them.¹

Can a multivitamin with selenium cause hair loss?

The sources checked link hair loss to long-term intakes well above the 55 mcg many multivitamins list. Selenium from several products and Brazil nuts can add up, so ask your doctor or pharmacist.^1,2

Does selenium sulfide shampoo cause hair loss?

The label read for this page does not list hair loss, and the NIH sheets do not cover selenium sulfide. The label says to stop use and ask a doctor if the condition worsens.⁵

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Sources

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.