Selenium is essential in small amounts, but too much of it causes hair loss rather than preventing it. Many hair, skin and nail supplements contain selenium, and people often take two or three products at once without adding up the dose. If shedding started after a new supplement routine, the first step is a review of everything you take, not another product.
Key points
In a 2008 United States outbreak reported in Archives of Internal Medicine in 2010, 201 people took a supplement containing 200 times its labelled selenium, and 72 percent developed hair loss.
The UK reference nutrient intake for selenium is 75 micrograms a day for men and 60 micrograms for women.
The European Food Safety Authority set the adult tolerable upper intake at 255 micrograms a day in 2023, well below many people's combined supplement total.
A 2019 review of vitamins and minerals in hair loss in Dermatology and Therapy found no evidence that selenium supplements help hair grow in people who are not deficient.
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How can a nutrient for normal health cause hair loss?
Selenium is a trace element the body uses to build antioxidant enzymes and thyroid hormones. A normal UK diet that includes fish, eggs, meat and wholegrains usually provides enough. Brazil nuts are unusually rich, and a single nut can contain more than a day's requirement.
The margin between enough and too much is narrow compared with most nutrients. When intake runs high for weeks, selenium builds up in tissues, including the hair follicle and nail bed. The result is a condition called selenosis.
The hair changes are the same type of shedding seen after illness or stress. Follicles are pushed early into their resting phase and the hairs fall out two to three months later. Hair can also become brittle and break near the scalp.
In the 2008 outbreak, 72 percent of affected people reported hair loss and 61 percent reported nail discolouration or brittleness. Hair loss persisted beyond 90 days in 29 percent. That outbreak involved enormous doses from a manufacturing error, but lower chronic excess can produce the same picture more slowly.
Why the whole supplement routine matters
Most cases of selenium excess we see do not come from one dramatic product. They come from layering. A multivitamin, a hair gummy, a thyroid support capsule and a handful of Brazil nuts can each look reasonable alone.
Added together, they can exceed the 255 microgram upper limit set by the European Food Safety Authority, before any selenium from food is counted. The older UK Expert Group on Vitamins and Minerals set a safe upper level of 450 micrograms a day from all sources, which some people still reach.
Labels make this harder than it should be. Selenium may appear as selenomethionine, sodium selenite or selenium yeast, and some products list it per serving while the directions suggest two or three servings.
The same layering applies to zinc, biotin and vitamin A, each of which can cause problems in excess. Vitamin A excess is itself a recognised cause of hair loss. Biotin does not usually harm hair, but high doses interfere with several blood tests, including thyroid tests, and can make results misleading.
A free supplement audit you can do tonight
This is the exercise our doctors ask every hair loss patient to complete before the first appointment. It is useful whether or not you ever see us.
Gather every supplement, powder, gummy and fortified drink you take, including ones you only use sometimes.
For each, find selenium on the label and note the amount per serving in micrograms.
Multiply by the number of servings you actually take each day.
Add a rough food figure. Each Brazil nut can contribute 50 micrograms or more, and an ordinary mixed diet often adds 40 to 60 micrograms.
Repeat the exercise for zinc, vitamin A and biotin.
Note the date you started each product and compare it with when shedding began. Shedding usually lags the trigger by two to three months.
If your selenium total is above 255 micrograms a day, stop the extra products and speak to a doctor. If shedding began two to three months after a new routine, that timing is a strong clue.
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Which symptoms make a review more important?
Hair loss alone has many causes, so the company it keeps matters. Selenium excess becomes more likely when shedding comes with any of the following.
Brittle, ridged or discoloured nails, or nails lifting from the bed.
A garlic smell on the breath that you cannot explain.
A metallic taste in the mouth.
Skin rash, fatigue, irritability or loose stools.
Tingling or numbness in the hands or feet.
Tingling, numbness, weakness or confusion need prompt medical assessment rather than a hair appointment. So does any rapid, patchy hair loss with smooth bald areas, which points to alopecia areata rather than a nutritional cause.
Most people with mild excess have only diffuse shedding and nail changes. Those are still worth checking, because the shedding will usually not settle until the intake comes down.
Can a selenium blood test give the answer?
A blood test helps, but it does not replace the supplement history. Serum or plasma selenium reflects recent intake and is useful for confirming a high level. In the 2008 outbreak, the mean initial serum selenium was 751 micrograms per litre against a reference limit of 125.
Milder chronic excess produces less dramatic numbers, and results can fall back towards normal within weeks of stopping. A normal result taken after you have already stopped does not rule out selenium as the cause of shedding that began months earlier.
That is why our doctors pair any selenium result with the standard hair loss panel. Ferritin, full blood count, thyroid function, vitamin D, B12 and folate cover the common, treatable causes of diffuse shedding. Hormone tests are added where the pattern or history suggests them.
If you take high-dose biotin, stop it for at least 48 to 72 hours before blood tests, or tell the doctor, because it can distort thyroid results.
Why a safe-intake figure is not a hair-growth dose
There is a common belief that if a little selenium is good for hair, more must be better. The evidence does not support it.
The 2019 review in Dermatology and Therapy by Almohanna and colleagues examined vitamins and minerals in hair loss. It found that selenium deficiency is rare in people eating a normal diet and that there is no good evidence selenium supplements improve hair in people who are not deficient. It also highlighted that excess selenium is itself a cause of hair loss.
The reference nutrient intake of 60 to 75 micrograms is what most people need. The upper limit is a ceiling for safety, not a target. Taking amounts near the ceiling brings risk without benefit.
As our doctors put it, "Most people who come to us taking six supplements for their hair need fewer, not more. The bloods tell us which one, if any, actually matters."
What happens to the hair-loss plan?
Where selenium excess is the likely cause, the plan starts with removing the extra source and waiting. Shedding usually slows over two to three months and regrowth follows over the next several months. Nails take longer, because they grow slowly.
During that time, a doctor checks for other causes running alongside. It is common to find low ferritin or an underlying pattern of genetic hair loss that the shedding has unmasked.
If genetic thinning is present, treatment may be discussed once the shedding has settled. Evidence-based options include topical or oral minoxidil, finasteride for men, and in suitable people PRP. Starting PRP during an active toxic shed rarely makes sense, because the trigger is still in place.
Where does PRP fit?
PRP has good evidence for genetic hair loss. A 2025 meta-analysis in Dermatology and Therapy pooled 43 randomised controlled trials with 1,877 participants and found PRP increases hair density, with greater gains when sessions were more frequent and when combined with minoxidil.
That evidence is for pattern hair loss, not for shedding caused by excess selenium. If the cause is a supplement, the answer is to stop the supplement. PRP becomes relevant later if thinning persists once the trigger has gone and bloods are normal.
You can read more in our guide to whether PRP works for hair loss.
What PRP and supplements cannot do
Neither PRP nor any supplement can override an ongoing trigger. If excess selenium, low iron or an untreated thyroid problem is driving shedding, treating the scalp first wastes time and money.
Selenium testing has limits. A single result reflects recent intake and can miss chronic excess after you have stopped.
The outbreak data come from very high doses. The evidence for lower-level chronic excess causing shedding is drawn from case reports and the known biology rather than large trials.
PRP does not suit everyone with thinning. It is less useful for scarring alopecias and for areas that have been bald for many years.
What does hair loss assessment and PRP cost in London?
Flagship Harley Street and Mayfair clinics commonly charge £600 to £850 or more per hair PRP session, and London practices generally charge 50 to 70 percent more than the rest of the UK. At the low end of the market, sessions are advertised from £150 to £300.
What the low-cost options usually omit is the diagnosis. No blood panel, no doctor reviewing your supplements, and no preparation protocol. For someone whose shedding is caused by a supplement, a session without that review is the wrong product at any price.
Our care is doctor-led and priced below flagship rates. The figure is confirmed at your free suitability review, after a doctor has looked at your history and bloods.
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Your free suitability review
Every enquiry starts with a free doctor-led suitability review rather than a booking. A GMC-registered doctor assesses you and gives one of two answers. Approved for treatment, with a clear plan and realistic expectations, or not approved, with an honest explanation of what would serve you better. We decline a meaningful share of enquiries, because treating someone who will not benefit helps nobody.
For suspected supplement-related shedding, a common outcome of the review is a plan that involves stopping products and repeating bloods, with no treatment booked. We would rather tell you that than sell a session that cannot work yet.
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Frequently asked questions
Can too much selenium cause hair loss?
Yes. Excess selenium, called selenosis, causes diffuse hair shedding, brittle hair and nail changes. In a 2008 outbreak involving a mislabelled supplement, 72 percent of 201 affected people developed hair loss. Lower chronic excess from layered supplements can cause the same pattern more slowly.
How much selenium is too much per day?
The European Food Safety Authority set the adult upper limit at 255 micrograms a day in 2023. The UK reference nutrient intake is 75 micrograms for men and 60 for women. Combined supplements and Brazil nuts can push daily intake past the upper limit.
Will hair grow back after stopping selenium?
In most people, yes. Shedding usually slows two to three months after the excess stops, and regrowth follows over several more months. If thinning persists, a doctor should check for iron deficiency, thyroid problems or genetic hair loss running alongside.
Do hair supplements with selenium work?
There is no good evidence that selenium supplements improve hair in people who are not deficient. A 2019 review in Dermatology and Therapy found deficiency is rare with a normal diet and that excess selenium is itself a cause of hair loss.
What blood tests check for selenium-related hair loss?
A serum or plasma selenium level confirms recent excess. Doctors usually add ferritin, full blood count, thyroid function, vitamin D, B12 and folate to rule out other common causes. A normal selenium after stopping does not exclude earlier excess.
Should I have PRP if supplements caused my hair loss?
Not while the trigger is still in place. Stop the excess supplement first and allow two to three months for shedding to settle. PRP may help later if genetic thinning persists, because its evidence is for pattern hair loss rather than toxic shedding.
This article is general information and does not replace a consultation with a doctor. If you have sudden severe pain, a hot swollen joint, fever or rapidly spreading redness, seek urgent medical care or call 999.
Reviewed by [GMC-REGISTERED DOCTOR NAME, GMC NUMBER TO CONFIRM], The London PRP Clinic by The Wellness. Last updated November 2026.