Can Hair Supplements Cause Hair Loss?The Selenium Problem
HairArticleSelenium shows up in hair, skin and nail blends, multivitamins and thyroid formulas, and Brazil nuts are packed with it. Too much over time can cause the very thing you're trying to fix: hair loss and brittle nails. Here is how to add up your intake from every source.
In this article
When hair starts thinning, it’s natural to stack up supplements: a hair, skin and nail blend, a multivitamin, maybe a thyroid support formula, plus a handful of Brazil nuts because you read they help. Many of these contain selenium, and getting too much of it over time can cause hair loss.1
Myth: more is better for your hair
Your thyroid needs selenium to make hormones.1 But too much selenium over time can cause:1
- hair loss
- brittle nails or nail loss
- garlic breath and a metallic taste
- skin rash, nausea, diarrhea
- extreme tiredness and irritability
- nerve problems
Very high amounts can cause serious problems, including kidney or heart failure.1
Brazil nuts add up fast
Brazil nuts contain very high amounts of selenium, roughly 68 to 91 micrograms in a single nut.1 Eating several a day, on top of supplements, can push you over the limit.1
How much is too much?
The U.S. upper limit for adults is 400 micrograms a day from all sources combined: food, drinks and supplements.1 European food safety experts set a lower limit of 255 micrograms in 2023.1 These limits don’t apply if a doctor has prescribed selenium for a medical reason.1
How to check your intake
- Gather every bottle you take: multivitamins, hair blends, thyroid formulas.
- Add up the selenium listed on each label, in micrograms.
- Count Brazil nuts as about 70 to 90 micrograms each.
- Bring the list to your pharmacist or clinician.2
Biotin isn’t the answer either
Biotin is also heavily marketed for hair, but there’s little scientific evidence for those claims, and high doses can throw off some lab tests.2 Our guides to biotin and hair vitamins and biotin and thyroid tests explain more.
What to do instead
Find out why your hair is thinning. Our guides to why hair thins, iron and hair loss and topical minoxidil cover causes and treatments with better evidence.
Try: “I take a hair supplement, a multivitamin and eat Brazil nuts most days. My hair is still thinning. Could I be getting too much selenium?”
Hair, Everywhere includes a Hair Check and a monthly Hair Log. Use them to list every supplement and dose alongside changes in your hair. See the book.
This article is for general educational purposes only and is not medical advice. It isn't a substitute for diagnosis or treatment from a qualified healthcare professional who knows your health history. Please don't ignore professional advice or delay getting care because of something you read here. If you take selenium on a doctor's advice, don't stop without asking. Seek urgent care for severe stomach upset, tremors, trouble breathing or chest pain after taking supplements. If you think you may be having a medical emergency, call 911 or your local emergency number right away. This article discusses supplement ingredients and federal health information. It does not evaluate any particular brand or product. Girl Playbook does not endorse any specific product, test, or provider.
Girl Playbook sells this book. It provides education and worksheets, not individualized medical care.
Sources
The research behind this article, in the order it’s cited. How we source our articles.
- Office of Dietary Supplements (NIH)Selenium: Fact Sheet for Consumers (opens in a new tab)abcdefghi
- NIHBiotin: Fact Sheet for Consumers (opens in a new tab)ab
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