Selenium and hair loss are more closely linked than many people realise. This essential trace mineral is required by the body in only tiny amounts, yet both too little and too much selenium can affect hair health. In the UK, selenium deficiency is uncommon in those eating a varied diet, but selenium toxicity — most often caused by high-dose supplementation — is a well-recognised trigger for diffuse hair shedding. Understanding the safe intake range, recognising the signs of overexposure, and knowing when to seek medical advice are all important steps if you are concerned about selenium and your hair.

Can Selenium Cause Hair Loss?

Selenium can cause hair loss in both deficiency and excess, but toxicity is the more consistent and clinically significant cause, pushing follicles prematurely into the telogen resting phase and resulting in diffuse shedding.

Not sure if this is normal? Chat with one of our pharmacists →

Selenium is an essential trace mineral that plays a role in thyroid hormone metabolism, antioxidant defence, and immune function. The body requires only very small amounts — typically measured in micrograms — and this narrow range means that both deficiency and excess can have health consequences, including effects on hair.

The relationship between selenium and hair loss works in both directions. Selenium deficiency has been associated with diffuse hair thinning in some observational studies and case reports, as the mineral is involved in the production of selenoproteins that support hair follicle cycling and protect cells from oxidative damage. However, this association is based largely on observational data and case reports; frank selenium deficiency is uncommon in the UK in people eating a varied diet, and it is rarely a primary cause of hair loss in this setting.

Selenium toxicity (selenosis) is more consistently linked to significant hair loss. Excess selenium is thought to disrupt the normal hair growth cycle, pushing follicles prematurely into the telogen (resting) phase — a process known as telogen effluvium — resulting in noticeable shedding. This is a proposed biological mechanism supported by case reports and outbreak data, rather than a definitively established pathway.

Clinical case reports and observational studies have documented hair loss as one of the earliest and most consistent signs of chronic selenium overexposure. This has been observed both in populations living in selenium-rich geographical areas and in individuals taking high-dose selenium supplements. A well-documented outbreak in the United States, reported by the CDC in 2008, involved a manufacturing error in a liquid selenium supplement; affected individuals experienced significant hair loss alongside other features of toxicity.

It is important to note that not all hair loss is selenium-related, and many other factors — including iron deficiency, thyroid disorders, hormonal changes, and stress — are far more common causes in the UK. Nevertheless, if you are taking selenium supplements and experiencing unexplained hair shedding, selenium intake is a reasonable factor to discuss with a healthcare professional.

Recommended Selenium Intake and Safe Upper Limits in the UK

The UK RNI is 75 µg/day for men and 60 µg/day for women; the EFSA tolerable upper intake level is 300 µg/day from all sources combined, and routine supplementation without clinical indication is generally unnecessary.

In the UK, dietary reference values for selenium are established by the Scientific Advisory Committee on Nutrition (SACN) and its predecessor the Committee on Medical Aspects of Food Policy (COMA), and are presented in NHS guidance. The Reference Nutrient Intake (RNI) — the amount considered sufficient for most of the population — is:

• 75 micrograms (µg) per day for adult men

• 60 µg per day for adult women

Most people in the UK obtain adequate selenium through their diet. Good dietary sources include:

• Brazil nuts (one of the richest natural sources — however, selenium content varies considerably between individual nuts and by growing region, so regular consumption of large quantities is not advisable)

• Seafood and fish (tuna, sardines, prawns)

• Meat and poultry

• Eggs and dairy products

• Wholegrains and cereals

The tolerable upper intake level (UL) set by the European Food Safety Authority (EFSA) — which informed UK guidance prior to and following EU exit — is 300 µg per day for adults from all dietary sources combined. The NHS advises that taking selenium supplements providing up to 350 µg per day is unlikely to cause harm, but cautions against exceeding this. These two figures reflect different methodological approaches; for practical purposes, keeping total daily intake (diet plus any supplements) at or below 300 µg per day is a reasonable and conservative target. Chronic intakes substantially above this level have been associated with selenosis in some individuals.

In the UK, food supplements — including selenium supplements — are regulated as foods under the Food Supplements (England) Regulations 2003 (and equivalent devolved legislation), with oversight by the Food Standards Agency (FSA) and local authorities. The Medicines and Healthcare products Regulatory Agency (MHRA) regulates medicines, not food supplements. There are no statutory maximum permitted levels for selenium specifically set in UK food supplement regulations; general food safety law applies.

If you take a multivitamin and mineral product alongside a separate selenium supplement, check the labels carefully to avoid inadvertently exceeding safe intake levels through double-dosing.

For most people eating a varied diet in the UK, selenium deficiency is uncommon, and supplementation is generally unnecessary unless advised by a clinician — for example, in confirmed deficiency, certain malabsorption conditions, or specific medical circumstances. Routine supplementation without clinical indication carries a real risk of inadvertent overexposure, particularly when dietary selenium intake is already adequate.

Signs You May Be Getting Too Much Selenium

Diffuse hair loss, brittle nails, and a garlic-like breath odour are characteristic early signs of selenium toxicity; if these occur alongside supplement use, stop the supplement and seek medical advice promptly.

Recognising the signs of selenium excess (selenosis) is important, particularly for individuals who take selenium supplements alongside a diet already rich in the mineral. Symptoms of chronic selenium toxicity can develop gradually and may initially be subtle, making them easy to overlook or attribute to other causes.

Hair and nail changes are among the most characteristic early signs:

• Diffuse hair loss or thinning, often noticed as increased shedding on the pillow, in the shower, or when brushing

• Brittle or fragile hair that breaks easily

• Nail brittleness, discolouration, or nails that separate from the nail bed (onycholysis)

• A garlic-like or metallic odour on the breath, caused by the exhalation of volatile selenium compounds

As toxicity progresses or intake remains high, additional symptoms may include:

• Nausea, diarrhoea, and gastrointestinal discomfort

• Fatigue and irritability

• Skin rashes or lesions

• Peripheral neuropathy — tingling, numbness, or pain in the hands and feet

• In rare cases of severe acute overdose, serious neurological symptoms may occur; if you suspect a large accidental ingestion, seek urgent medical attention

It is worth noting that there is no established link between selenium at recommended dietary levels and hair loss in otherwise healthy individuals. The concern arises specifically with supplemental overuse or unusually high dietary intake — for instance, consuming large quantities of Brazil nuts daily over a prolonged period, noting that selenium content in Brazil nuts varies widely.

If you are currently taking a selenium supplement and notice any of the above symptoms, it is advisable to stop the supplement and seek medical advice promptly. If selenium was prescribed by a clinician (for example, for a confirmed deficiency or as part of nutritional support), seek advice before stopping rather than discontinuing without guidance. Serum or plasma selenium levels can be measured to confirm whether overexposure is occurring, and a clinician can help identify whether selenium is the likely cause of your symptoms.

If you believe you have experienced a side effect from a selenium supplement, you can report this to the MHRA via the Yellow Card Scheme (yellowcard.mhra.gov.uk).

Experiencing these side effects? Our pharmacists can help you navigate them →

When to Speak to a GP About Hair Loss and Supplements

See your GP if hair loss is significant, rapidly worsening, or accompanied by other symptoms such as fatigue, nail changes, or a garlic-like breath odour, particularly if you have recently started a selenium supplement.

Hair loss can be distressing, and while it is often benign and self-limiting, it can sometimes signal an underlying health condition that warrants investigation. If you are experiencing noticeable hair shedding — particularly if it is sudden, diffuse, or accompanied by other symptoms — it is worth discussing this with your GP rather than self-diagnosing or adjusting supplements without guidance.

You should contact your GP if you notice:

• Significant or rapidly worsening hair loss that is affecting your confidence or daily life

• Hair loss alongside fatigue, weight changes, or feeling unusually cold — which may suggest a thyroid disorder

• Nail changes, skin symptoms, or a persistent garlic-like breath odour alongside hair shedding

• Hair loss that has developed after starting a new supplement regimen

• Any symptoms consistent with selenium toxicity as described above

Seek prompt or urgent assessment if you notice:

• A painful, inflamed, or scarred scalp, or areas of permanent-looking hair loss — these may suggest scarring alopecia, which requires timely specialist assessment to prevent irreversible follicle damage

• Patchy hair loss with scaling, pustules, or broken hairs, particularly in a child — this may indicate tinea capitis (scalp ringworm) or a kerion, which require prompt review and treatment

Your GP may arrange blood tests to investigate potential causes. Core first-line investigations typically include:

• Full blood count (to check for anaemia)

• Thyroid function tests (TSH, with free T4 if indicated)

• Ferritin and iron studies

• Serum or plasma selenium levels, if toxicity or deficiency is clinically suspected

Additional tests — such as vitamin D, B12, or folate — may be considered if there is a specific clinical reason, but are not routinely indicated for hair loss without supporting symptoms or risk factors.

For assessment and management of telogen effluvium in primary care, the Primary Care Dermatology Society (PCDS) provides practical UK guidance. NICE Clinical Knowledge Summaries (CKS) on alopecia areata offer further guidance on investigation and referral pathways for that specific condition. If a selenium supplement is identified as a contributing factor, your GP will advise on stopping or reducing the dose and monitoring for recovery — hair regrowth following telogen effluvium typically begins within three to six months of removing the trigger.

It is always advisable to inform your GP of all supplements you are taking, including vitamins and minerals, and to check that you are not taking more than one selenium-containing product concurrently. Self-prescribing high-dose micronutrient supplements without clinical oversight carries risks that are often underestimated, and professional guidance ensures your approach to supplementation is both safe and evidence-based.

Frequently Asked Questions