Vitamin A is involved in the maintenance and function of epithelial tissues, including the skin and hair. Scientifically, vitamin A is essential for cellular growth and differentiation, which are critical for the normal cycling of hair follicles. Studies have shown that vitamin A regulates the production of sebum, an oily substance produced by sebaceous glands in the scalp, which helps keep hair moisturized and healthy. Severe deficiency in vitamin A can result in hair thinning and hair loss, as observed in clinical cases of malnutrition or vitamin A deficiency. Animal studies also demonstrate that either a deficiency or excess of vitamin A can lead to hair follicle dysfunction.

However, while vitamin A is necessary for normal hair growth, there is limited direct evidence that supplementation in people with adequate intake provides additional benefits for hair health or growth. In fact, excessive intake of vitamin A can lead to toxicity, which may cause hair loss. Most research supports the role of vitamin A in preventing deficiency-related hair problems, rather than as a treatment for common hair loss in otherwise healthy individuals. Thus, while vitamin A's role in supporting the hair body system is validated scientifically, its use is best justified as part of a balanced diet rather than as a targeted supplement unless a deficiency is diagnosed.