How does retinol improve scalp health and prepare the skin for other hair growth treatments?

Retinol, known primarily for its benefits on facial skin, is drawing increasing attention for its effects on the scalp. When applied to the scalp, retinol is converted by the body into retinoic acid, a biologically active molecule that influences cellular growth, differentiation and communication. The goal of this article is to critically examine how retinol and retinoic acid improve scalp biology and prepare the skin for hair growth treatments such as minoxidil. This analysis focuses on the evidence available in scientific literature and what we, as patients and informed readers, need to know to understand what is happening on the scalp when these compounds are applied.

Retinol and Cellular Renewal in the Scalp

Retinol supports the natural process of epidermal turnover, helping remove excess dead skin cells and residues that accumulate on the scalp. This is relevant because the outermost layer of the skin, the stratum corneum, can become compacted due to oil production, styling products and pollution. When this layer becomes excessively dense, it creates an occlusive environment that can hinder the exchange of nutrients and oxygen to the hair follicle.

According to Typology, retinol does not function as a traditional keratolytic like acids, but it accelerates the process of desquamation by stimulating skin cells to renew faster. This has implications for the scalp because it can lead to a cleaner surface where hair follicles are less obstructed, creating conditions that are more favorable to normal follicular physiology. In simpler terms, the scalp becomes less congested, which can reduce inflammation and irritation that many patients with thinning hair experience.

Activation of Hair Follicle Stem Cells

A 2024 study published in the Journal of the European Academy of Dermatology and Venereology investigated the effects of retinoic acid on human and mouse hair follicles. Researchers used microdissected human scalp follicles and also worked with mouse follicles in the resting (telogen) phase. The study lasted several days in culture and evaluated markers of cellular activity and signaling pathways. They found that retinoic acid stimulated hair follicle stem cells and promoted transition into the active growth phase, known as anagen. The activation was associated with the Wnt/β‑catenin signaling pathway, which plays a central role in controlling whether hair follicles remain at rest or begin producing new hair fibers.

For those of us seeking treatment, this finding matters because androgenetic alopecia is characterized by reduced stem‑cell activity. If retinoic acid can help restore this activation, it may support hair follicles that are becoming progressively miniaturized.

Enhancement of Other Hair‑Growth Treatments

Minoxidil is one of the most frequently prescribed topical treatments for pattern hair loss. Retinoic acid has been studied as a potential enhancer of minoxidil’s effects. A 2007 study on human hair follicles grown in vitro found that combining minoxidil with all‑trans retinoic acid resulted in greater hair shaft elongation than minoxidil alone. The experiment ran for 12 days and evaluated molecular activity related to cell survival and growth. The combination increased phosphorylation of the Erk and Akt pathways, which are associated with cellular proliferation and longevity, and also increased the ratio of Bcl‑2 to Bax, a marker suggesting reduced programmed cell death.

This means that the combination does not merely change the hair cosmetically but affects the underlying cellular machinery. For those using minoxidil who have not responded as expected, retinoic acid may be a factor that increases follicular responsiveness. However, the evidence is laboratory‑based and may not fully translate to clinical outcomes.

A clinical study published in 1986 examined 56 patients with androgenetic alopecia treated for one year with topical tretinoin alone or combined with minoxidil. The combination demonstrated higher hair regrowth rates compared to tretinoin alone. This reinforces the laboratory findings and suggests that, for some individuals, retinoic acid may increase the therapeutic potential of minoxidil. However, tretinoin alone also showed notable regrowth, which suggests that some of its benefits extend beyond absorption enhancement.

One of the documented biological effects of retinoic acid is that it increases epidermal permeability. This is part of the reason it may improve the absorption of other treatments. A 2014 mouse study found that minoxidil combined with topical tretinoin increased follicle diameter, but this effect was dose‑dependent. Higher concentrations of tretinoin did not enhance results and even reduced the benefit, indicating a narrow therapeutic window.

Greater skin permeability can help beneficial substances penetrate the follicular canal, but it can also allow irritation or damage if the concentration is too high or combined with other aggressive agents. This aspect is important when evaluating retinoic acid from a patient perspective because the line between therapeutic improvement and excessive stimulation is thin.

Evidence of Potential Negative Effects

Retinoic acid is not universally beneficial and can induce negative outcomes under certain conditions. A 2005 study using human scalp follicles grown in vitro found that exposure to retinoic acid at concentrations of 10⁻⁸ to 10⁻¹⁰ M resulted in premature entry into the catagen phase, which is the regression stage of the follicle cycle. This response occurred within six days and was associated with increased expression of transforming growth factor‑beta 2 in the dermal papilla. TGF‑β2 is known to push follicles toward regression, meaning that excessive or improperly dosed retinoic acid can have the opposite of the desired effect.

From a practical standpoint, this finding indicates that while retinoic acid can activate stem cells and enhance growth pathways, it can also suppress growth if exposure is too intense. This duality is not unique to retinoic acid, but it means that the dose, frequency of application and the biological context of the scalp matter.

What We Need to Know as Patients

**When evaluating whether to use retinol or retinoic acid on the scalp, the most important takeaway is that the compound does not act uniformly. ** It may increase cellular activity, improve absorption of other treatments and help follicles re‑enter the anagen phase. However, it can also induce regression if misused. Therefore, the question we should be asking is not whether retinol “works” but under what conditions it is beneficial.

For individuals experiencing androgenetic alopecia, there are several biological implications. Retinoic acid may help counteract the reduced stem‑cell activation seen in follicular miniaturization. It may also increase the effectiveness of minoxidil if follicles are otherwise unresponsive. Conversely, if excessive concentrations push follicles toward catagen, some users may find hair shedding increases rather than decreases.

In short, understanding the mechanisms and the evidence helps us make informed decisions about what is happening to our scalps when we apply retinol‑based products.

Retinol and its active metabolite retinoic acid exert multiple biological effects on the scalp. They influence epidermal turnover, hair follicle stem‑cell activity and absorption of other therapeutic agents.

Evidence from laboratory and clinical studies indicates that retinoic acid can improve conditions for hair growth and enhance the response to minoxidil. However, the benefits depend on dose and exposure, and research also shows that improperly applied retinoic acid can trigger premature follicular regression.

For readers and patients seeking treatment, the key is that the biological effects of retinol are real, measurable and complex. Understanding them allows us to evaluate whether a topical retinoid is a useful addition to a hair‑growth regimen and what risks may accompany its use.

References

Li, J., Guo, S., Wang, C., Zhang, L., Li, Y., & Li, G. (2024). Retinoic acid drives hair follicle stem cell activation via Wnt/β‑catenin signalling in androgenetic alopecia. Journal of the European Academy of Dermatology and Venereology. Retrieved from https://pubmed.ncbi.nlm.nih.gov/38629345/

Yang, C. C., Lin, T. Y., & Liu, J. S. (2007). The additive effects of minoxidil and all‑trans retinoic acid on human hair growth in vitro. Journal of the American Academy of Dermatology. Retrieved from https://pubmed.ncbi.nlm.nih.gov/17449938/

Ong, D. E., et al. (1986). Topical tretinoin for hair growth promotion. Journal of the American Academy of Dermatology. Retrieved from https://www.sciencedirect.com/science/article/pii/S019096228680024X

Paus, R., Foitzik, K., Eichmüller, S., Handjiski, B., et al. (2005). Premature catagen induced by retinoic acid