What’s the difference between retinol and salicylic acid in scalp care and follicle renewal?

Retinol and salicylic acid both appear in scalp products, and both are often described as "renewing" the scalp. They work in different ways, have different evidence behind them, and carry different safety points. Neither has been shown to regrow hair or to "renew" hair follicles in people.

Salicylic acid: loosening scale on the surface

Salicylic acid works on the outermost layer of the skin. A dermatology review describes it as loosening the bonds between surface skin cells so that they shed more easily, and notes its use in acne because it helps clear blocked pores (Arif 2015). US labelling describes it as producing shedding of the horny layer of the skin without changing the living layers beneath (DailyMed, salicylic acid 6% shampoo label).

On the scalp, its main established use is scale. The US over-the-counter rules allow salicylic acid at 1.8 to 3 percent in products for the control of dandruff (21 CFR 358.710). Higher-strength prescription products are labelled for thick, scaly conditions such as scalp psoriasis (DailyMed, salicylic acid 6% shampoo label). There is no evidence that salicylic acid makes hair grow.

Safety points from the label: do not use it if you are sensitive to salicylic acid or other salicylates; avoid the eyes; prescription 6% products should not be used in children under 2. Using it over large areas for a long time, especially in children or people with kidney or liver problems, can cause salicylate poisoning (salicylism). The label also warns against adding aspirin or other salicylate products at the same time, and says salicylate products should not be used in children and teenagers with chickenpox or flu unless a doctor directs it, because of the risk of Reye’s syndrome (DailyMed, salicylic acid 6% shampoo label).

Retinol: acting on how skin cells grow

Retinol is a form of vitamin A. Retinoids bind to receptors inside skin cells and change how the cells multiply and mature (Motamedi et al. 2022). Rather than thinning the skin, topical retinoids thicken the outer layer of the epidermis (Rittié et al. 2006). They commonly cause redness, dryness and peeling.

The hair research on retinoids used prescription tretinoin (all-trans retinoic acid), mostly on follicles in the lab or in mice, not over-the-counter retinol. The results point both ways: one study suggested retinoic acid can activate hair follicle stem cells (Wen et al. 2025), while another found it pushed about 80% of cultured human scalp follicles into early regression (catagen) within six days, compared with 30% of untreated follicles (Foitzik et al. 2005). No trial has tested retinol for hair loss.

Pregnancy. Oral isotretinoin causes severe birth defects and is contraindicated in pregnancy (US label boxed warning), and it can cause hair loss that sometimes persists (DailyMed, Amnesteem label). For topical retinoids, a meta-analysis of 654 exposed pregnancies found no statistically significant rise in major birth defects (odds ratio 1.22, 95% CI 0.65–2.29), but the authors say it was too small to show that using them in pregnancy is safe (Kaplan et al. 2015). People who are pregnant, trying to conceive or breastfeeding should not use retinoids on the scalp without medical advice. Tretinoin is a prescription medicine.

Side by side

• Where it acts: salicylic acid works on surface scale; retinoids change how skin cells grow and mature.
• Established scalp use: salicylic acid is an approved over-the-counter dandruff ingredient; retinol has no established scalp use.
• Hair growth: no evidence for either in people.
• Main cautions: salicylic acid — salicylate allergy, children, large areas, other salicylates; retinoids — irritation and pregnancy.

Using both at once may add to irritation. If flaking, itching or thinning is the problem, a dermatologist can check the cause before you choose a product.

References

Arif, T. (2015). Salicylic acid as a peeling agent: a comprehensive review. Clinical, Cosmetic and Investigational Dermatology, 8, 455–461. https://pubmed.ncbi.nlm.nih.gov/26347269/

DailyMed. Salicylic Acid 6% (w/w) Shampoo prescribing information. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=b66252b0-84b5-45fc-a5f4-fd35dd341e73

U.S. Code of Federal Regulations. 21 CFR 358.710 — Active ingredients for the control of dandruff, seborrheic dermatitis, or psoriasis. https://www.ecfr.gov/current/title-21/section-358.710

Motamedi, M., Chehade, A., Sanghera, R., & Grewal, P. (2022). A clinician’s guide to topical retinoids. Journal of Cutaneous Medicine and Surgery, 26(1), 71–78. https://pubmed.ncbi.nlm.nih.gov/34292058/

Rittié, L., Varani, J., Kang, S., Voorhees, J. J., & Fisher, G. J. (2006). Retinoid-induced epidermal hyperplasia is mediated by epidermal growth factor receptor activation via induction of heparin-binding EGF and amphiregulin in human skin in vivo. Journal of Investigative Dermatology, 126(4), 732–739. https://pubmed.ncbi.nlm.nih.gov/16470170/

Wen, L., Fan, Z., Huang, W., et al. (2025). 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, 39(1), 189–201. https://pubmed.ncbi.nlm.nih.gov/38629345/

Foitzik, K., Spexard, T., Nakamura, M., Halsner, U., & Paus, R. (2005). Towards dissecting the pathogenesis of retinoid-induced hair loss: all-trans retinoic acid induces premature hair follicle regression (catagen) by upregulation of transforming growth factor-beta2 in the dermal papilla. Journal of Investigative Dermatology, 124(6), 1119–1126. https://pubmed.ncbi.nlm.nih.gov/15955085/

Kaplan, Y. C., Ozsarfati, J., Etwel, F., et al. (2015). Pregnancy outcomes following first-trimester exposure to topical retinoids: a systematic review and meta-analysis. British Journal of Dermatology, 173(5), 1132–1141. https://pubmed.ncbi.nlm.nih.gov/26215715/

DailyMed. Amnesteem (isotretinoin capsules) prescribing information. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=b2cb63c9-f825-4991-9a2c-6260f1bbcc2c