Protein is scientifically validated as important for supporting hair health and potentially addressing hair loss or thinning, especially when the cause is related to dietary protein deficiency. Hair is primarily composed of keratin, a fibrous protein. Adequate protein intake provides the necessary amino acids for keratin production and hair follicle function. Scientific studies have shown that insufficient protein can lead to telogen effluvium, a form of diffuse hair shedding, which is reversible with the restoration of normal protein intake. Clinical observations and nutritional studies reinforce that individuals with protein malnutrition, such as in kwashiorkor or restrictive dieting, often experience hair thinning and loss.

However, for individuals who already consume sufficient protein, there is limited evidence that further increasing protein intake will enhance hair growth or prevent hair loss due to other causes (e.g., androgenetic alopecia, autoimmune conditions). Topical application of protein or protein-rich products (like keratin treatments) may temporarily improve the appearance or texture of hair but do not address the underlying biological processes of hair growth.

In summary, adequate dietary protein is scientifically supported as essential for maintaining healthy hair and preventing loss from deficiency. Its role is less clear or unsupported in treating other forms of hair loss not related to nutrition.