Is Selenium More Effective When Taken Orally or Applied Topically in Shampoos or Serums?

Scientific Context and Why This Matters

Selenium is a trace mineral that our bodies require in very small amounts. In nutrition science, “trace” means the element is essential but needed only in tiny quantities to maintain normal physiological functions. Selenium is best known for being part of enzymes called selenoproteins, including glutathione peroxidases, which protect cells from damage caused by oxidative stress, a term referring to harmful chemical reactions involving free radicals that can damage cells and tissues. **Selenium’s role extends to thyroid regulation, immune support, and antioxidant activity, but it also has a narrow margin between beneficial and harmful doses. **

When intake is too high, it can lead to toxicity with symptoms such as hair loss, nail brittleness, and neurological signs. Research from authoritative nutrition sources confirms that most healthy adults meet their selenium needs from diet alone and that chronic high intake causes toxicity rather than benefit. In the context of hair and scalp health, people often conflate selenium’s general physiological importance with the specific question of whether it supports hair growth, whether through oral supplements or topical applications such as shampoos or serums. This article examines scientific evidence, clarifies confusion around different forms of selenium, and explains what research supports or contradicts common claims.

Oral Selenium Supplements: What Evidence Actually Shows

The idea behind taking selenium orally — meaning consuming pills or dietary supplements — is that additional selenium might correct a deficiency and thereby improve body functions that depend on selenium. However, the scientific evidence related to hair specifically is far more nuanced than many marketing claims suggest. In the most comprehensive reviews of micronutrient supplements and hair health, researchers have found no consistent high-quality evidence showing that selenium supplementation prevents hair loss or stimulates hair growth in people with normal selenium status. In a systematic review of nutrients and hair loss, the authors highlighted that while deficiencies (such as iron deficiency) can cause hair loss, evidence supporting supplementation with selenium — especially in people without deficiency — is weak and sometimes contradictory. They also noted that over-supplementation of selenium, along with certain vitamins like A and E, has been linked to hair loss rather than improvement.

More direct analyses support this conclusion. The Office of Dietary Supplements at the National Institutes of Health (NIH) confirms that selenium deficiency is rare in well-nourished populations and that chronic high intake can lead to a condition called selenosis, which is characterized by hair loss as one of its primary symptoms. In this context, hair loss does not represent a therapeutic effect but rather a toxicity effect when selenium intake far exceeds normal dietary levels.

There are isolated reports in the medical literature suggesting that selenium supplements may cause hair loss and nail dystrophy (abnormal nail growth or breakage), further emphasizing that excess selenium does not improve hair health and may actually harm it. In a review focusing on alopecia (hair loss), researchers specifically noted there is no consistent evidence supporting a connection between serum selenium levels and hair loss conditions such as alopecia areata, and that indiscriminate supplementation could do more harm than good without proper clinical assessment.

In summary, oral selenium supplements do not have reliable clinical evidence supporting hair growth benefits in individuals with adequate selenium status, and excessive intake is clearly linked to adverse effects including hair loss due to toxicity.

Topical Selenium

Topical selenium refers to selenium compounds applied directly to the scalp, such as in medicated shampoos or serums. The most studied form of topical selenium is selenium disulfide (sometimes referred to scientifically as SeS₂). Importantly, selenium disulfide is a chemical compound distinct from nutritional selenium and does not function as a nutrient when applied to the skin. Instead, it acts primarily as an antifungal and seborrheic dermatitis therapy. Diseases such as dandruff and seborrheic dermatitis involve overgrowth of certain fungi and imbalances in the microbiome (the community of microorganisms that live on the scalp). Selenium disulfide’s primary mode of action is to inhibit fungi like Malassezia, which thrive on oily scalps and contribute to flaking and inflammation. It also helps modulate bacterial populations and sebum composition, leading to improvements in visible flaking and scalp condition.

Several clinical studies support these targeted effects. In a 6-week clinical trial with 93 adult participants of various hair types (including different curl patterns and skin phototypes), selenium disulfide shampoo applied twice weekly significantly reduced dandruff severity, erythema (redness), itching, and total dandruff scores. The study also showed that selenium disulfide rebalanced the scalp microbiome, meaning it altered fungal and bacterial populations toward healthier proportions. Participants consistently reported tolerability and cosmetic acceptability, and objective measures confirmed these improvements over baseline.

Another randomized clinical study compared 1 % selenium disulfide shampoo with 2 % ketoconazole shampoo over 4 weeks in adults with moderate to severe seborrheic dermatitis. Both treatments significantly improved clinical scores for flaking, redness, and irritation, with no major difference in efficacy, though selenium disulfide shampoo showed higher cosmetic acceptance. These outcomes demonstrate that selenium disulfide performs comparably to established antifungal treatments used for scalp dermatitis, which indirectly improves scalp health — though not necessarily hair growth per se.

Longer observational studies involving over a thousand subjects also showed that regular use of selenium disulfide shampoos was associated with significant improvements in flaking, itching, and erythema after 4 weeks, with high satisfaction and good tolerance.

The scientific consensus from these clinical evaluations is that selenium disulfide shampoos improve scalp conditions linked to fungal overgrowth and inflammation, providing a clearer and less irritated scalp environment. A healthier scalp environment may indirectly benefit hair retention, but there is no credible evidence that selenium disulfide penetrates deeply enough to stimulate hair follicles directly and induce new hair growth.

Risks and Misconceptions: Tears Between Topical Use and Oral Nutrition

It is critical to underscore that selenium disulfide shampoos do not supply nutritional selenium into the body. Their mechanism is local, acting on the scalp surface and superficial layers of skin. Systemic absorption in normal use is minimal. Therefore, while such shampoos can help treat dandruff or dermatitis symptoms, they don’t confer nutritional benefits to hair follicles from within the bloodstream. Conversely, oral selenium supplementation affects the entire body, but there is no strong evidence that it improves hair growth unless a person has a true selenium deficiency — a condition that is rare in developed countries. Moreover, because the range between essential and toxic intake is narrow, excessive selenium consumed orally can result in selenosis with hair loss and other clinical symptoms of toxicity.

The confusion between topical and nutritional selenium stems partly from the fact that products marketed for hair health often list “selenium” without clarifying the chemical difference between nutritional forms (like selenomethionine) and medicinal forms (like selenium disulfide). Scientifically, these serve very different purposes, and confusing them leads to misleading expectations about what benefits they might provide.

Scientific Conclusion: What Does the Evidence Really Say?

1. Oral selenium supplements have no reliable evidence supporting hair growth enhancement in people with normal selenium status. They may be necessary for rare cases of genuine deficiency, but beyond that, they can cause toxicity including hair loss.

2. Topical selenium disulfide shampoos are effective in managing scalp conditions like dandruff and seborrheic dermatitis through antifungal activity and microbiome rebalancing. These improvements benefit scalp health and comfort but do not directly stimulate hair growth at the follicle level.

Therefore, the answer to the fundamental question is that selenium’s effectiveness depends on the purpose. For scalp condition management, topical selenium disulfide shampoos have strong clinical support. For nutritional hair growth support, oral selenium has no well-substantiated benefit in the absence of deficiency and carries risk when consumed in excess.

References

Deloche-Bensmaine, C., Kovylkina, N., Faure, J., Clavaud, C., & Gueniche, A. (2025). A selenium disulfide-based shampoo is beneficial for dandruff management and rebalancing the scalp microbiome of subjects of any hair type. Skin Appendage Disorders. https://pmc.ncbi.nlm.nih.gov/articles/PMC12084028/

International multicenter study on selenium disulfide-based shampoo efficacy. (2024). PubMed. https://pubmed.ncbi.nlm.nih.gov/37098775/

Comparative randomized clinical study assessing the efficacy of a 1 % selenium disulfide-based shampoo versus 2 % ketoconazole shampoo. (2024). PubMed. https://pubmed.ncbi.nlm.nih.gov/39659649/

Office of Dietary Supplements. (2025). Selenium health professional fact sheet. National Institutes of Health. https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/

Office of Dietary Supplements. (2025). Selenium consumer fact sheet. National Institutes of Health. https://ods.od.nih.gov/factsheets/Selenium-Consumer/

Guo, E. L., & Katta, R. (2017). Diet and hair loss: Effects of nutrient deficiency and supplement use. PubMed Central. https://pmc.ncbi.nlm.nih.gov/articles/PMC5315033/

Civas, E., & Akpınar, Ü. (2024). Selenium in the supplement as the probable cause of hair loss and nail dystrophy. Journal of Cosmetic Dermatology. https://pubmed.ncbi.nlm.nih.gov/37594173/

Association between selenium and alopecia: evidence review. (2018). PubMed Central. https://pmc.ncbi.nlm.nih.gov/articles/PMC5939011/

Selenium disulfide topical uses and side effects. (n.d.). Wikipedia. https://en.wikipedia.org/wiki/Selenium_disulfide