Selenium is a trace mineral that plays a crucial role in various biological processes, including antioxidant defense and thyroid hormone metabolism, both of which can impact hair health. Scientific studies suggest that selenium is essential for the proper functioning of selenoproteins, which help protect cells from oxidative damage. This is relevant to hair because oxidative stress can contribute to hair loss and poor hair quality.

Selenium deficiency has been linked to several forms of hair loss, most notably in cases of severe deficiency where individuals may develop a condition called "telogen effluvium," characterized by diffuse hair shedding. Additionally, selenium is important for the synthesis of thyroid hormones; thyroid dysfunction, in turn, is a well-known cause of hair loss. However, it is important to note that while adequate selenium levels are necessary for hair health, excessive intake can also cause hair loss and other toxic effects.

Overall, current scientific evidence supports the role of selenium as a necessary micronutrient for maintaining healthy hair, particularly in cases of deficiency. However, there is limited evidence that selenium supplementation improves hair growth or quality in individuals who already meet their dietary requirements. The scientific evidence is moderate, and selenium should be used with caution to avoid toxicity.