The benefits of retinol for hair.

The retinol, the alcoholic form of vitamin A, is primarily known for its skin benefits. It has been used in dermatology for several decades for its ability to stimulate cell renewal as well as the synthesis of collagen and elastin by fibroblasts. These properties make retinol a staple in treatments targeting imperfections, skin sagging, or even pigmented spots. When applied to the skin, retinol is first converted into retinal, also called retinaldehyde, before being transformed into retinoic acid, its biologically active form. However, beyond the skin, the properties of retinol are generating increasing interest in the hair care field.

• Retinol has a purifying effect on the scalp.
  Just like the skin on the face and the rest of the body, the scalp skin requires regular exfoliation. It is indeed important not to let impurities accumulate to prevent the obstruction of hair follicles, which can hinder hair growth, as well as the occurrence of dandruff, which is the result of a disruption in cell renewal. While retinol does not have a keratolytic effect per se, it accelerates the elimination of cells from the horny layer, thus preventing them from accumulating and forming clusters, that is, dandruff.

The retinol remains a potentially irritating and drying substance. It is generally recommended for scalps with a tendency to be oily, whether or not they have dandruff.

• Retinol might promote hair growth.
  Some studies also suggest that retinol could stimulate hair growth and that it could potentiate the effects of minoxidil, a medication used in androgenetic alopecia. In 2007, a study in vitro tested this combination on human hair follicles incubated for 12 days. The researchers compared the growth achieved with minoxidil alone (1 µM) to that observed with the addition of retinol (17 nM). A significantly greater hair growth was measured for the group receiving the combination.

  Another study, conducted on 56 individuals with androgenetic alopecia, evaluated the effect of topical tretinoin, either alone or in combination with a 0.5% minoxidil solution, on hair regrowth. After one year, the combination of the two molecules allowed hair regrowth in 66% of the participants. Used alone, tretinoin led to improvement in about 58% of them. A notable case involves a woman suffering from severe alopecia for over 20 years who observed regrowth only with tretinoin after 18 months of use. Tretinoin appears to work by stimulating cell proliferation and differentiation at the epidermis level, as well as local vascularization — two essential mechanisms for supporting hair growth. These encouraging results deserve further exploration, particularly to better understand the potential role of retinoids alone or in synergy with low concentration minoxidil

Note : Consuming excess vitamin A orally can have the opposite effect and lead to hair loss. Indeed, an overload of this vitamin can exceed the capacity of the liver's transport system, leading to uncontrolled release into the bloodstream. This disrupts the homeostasis of active metabolites and triggers a premature transition to the telogen phase, which is the hair shedding phase.

Several clinical cases illustrate the harmful effects on hair due to an excess of Vitamin A. In 1979, a woman undergoing dialysis experienced hair loss related to her daily intake of 5000 IU of Vitamin A. Her serum levels were extremely high, and discontinuing the supplement allowed her to return to normal within a month. In another case, a 60-year-old man developed non-scarring fronto-central alopecia, along with loss of pubic and axillary hair, following excessive Vitamin A supplementation.

This is among the reasons why it is recommended to not exceed 3,000 µg/day for adults.