Retinoic Acid has been shown to alter collagen synthesis, increase dermal hyaluronic acid levels, and stimulate fibroblast growth and extracellular matrix formation. It is used to treat keratinization disorders and acne. The anti-ageing effect of retinoic acid has been well-researched and reported, and it is often used to treat the visual signs of ageing, it can take up to 6 months to see these effects. It is linked to a variety of side effects, including itching, photosensitivity, skin dryness, redness, and peeling.

Ref:
Creidi P, Vienne MP, Ochonisky S, Lauze C, Turlier V, Lagarde JM, Dupuy P. Profilometric evaluation of photodamage after topical retinaldehyde and retinoic acid treatment. J Am Acad Dermatol. 1998 Dec;39(6):960-5. doi: 10.1016/s0190-9622(98)70270-1. PMID: 9843009.

Mukherjee S, Date A, Patravale V, Korting HC, Roeder A, Weindl G. Retinoids in the treatment of skin aging: an overview of clinical efficacy and safety. Clin Interv Aging. 2006;1(4):327-48. doi: 10.2147/ciia.2006.1.4.327. PMID: 18046911; PMCID: PMC2699641.

Duell EA, Kang S, Voorhees JJ. Unoccluded retinol penetrates human skin in vivo more effectively than unoccluded retinyl palmitate or retinoic acid. J Invest Dermatol. 1997 Sep;109(3):301-5. doi: 10.1111/1523-1747.ep12335788. PMID: 9284094.

Fluhr JW, Vienne MP, Lauze C, Dupuy P, Gehring W, Gloor M. Tolerance profile of retinol, retinaldehyde and retinoic acid under maximized and long-term clinical conditions. Dermatology. 1999;199 Suppl 1:57-60. doi: 10.1159/000051381. PMID: 10473963.