ACTION MECHANISMS / PROOFS OF EFFECTIVENESS
Zinc is a powerful 5α-reductase inhibitor [2, 3]. This enzyme catalyzes the conversion of androgens into DHT (dihydrotestosterone), which fixes on to the receptors located on the sebaceous glands. This fixation brings about sebum production. By inhibiting this enzyme, zinc alleviates hyperseborrhea.
In vivo tests have confirmed this action in zinc . Measurement of sebum production on the skin’s surface during topical treatment containing zinc shows a reduction in the quantity of sebum produced.
Moreover, zinc ions exert an anti-inflammatory action. Indeed, on keratinocyte cultures, zinc reduces activation of these same cells. It reduces the production of TNF-α and maintains cell viability .
In vitro, zinc brings about a reduction in oxidative stress. It is therefore part of the large family of antioxidants. Firstly, it is thought to form mercaptides with the thiol groups in the protein membranes, thus preventing the formation of free radicals with other metal ions. In addition, it is thought to maintain the activity and structure of superoxide dismutase. Finally, it is thought to increase the concentration of metallothioneins, which destroy free radicals .
Zinc is also known for its antiseptic activity. Studies have been conducted on cultures of microorganisms such as E. Coli, S. Aureus and C. Albican. These show that zinc has the ability to inhibit bacterial and fungistatic proliferation .
Finally, a cicatrizing action has been shown [6, 7].
OUR EXPERT’S OPINION
As a 5-α-reductase modulator, zinc is well known and established. It also has an antimicrobial activity, which is variable, however, depending on the form of salt used and its associations (copper, for example).
Its recommendation for acne-prone oily skin is customary.
Its availability continues to be an issue. “Organic” salt forms are preferable to mineral salts. Salicylate, acetate and gluconate are the ones most generally used.
Owing to its chelating character, zinc may also interact with certain formula excipients (free doublets like hydroxyls) and find itself trapped in complexes that have to be exchanged in the biological environment. As a precautionary measure, this should therefore be confirmed by testing.
A concentration of 3% could be interesting for its gluconate form. However, we must have a measured expectation on the activity obtained in the short term in all cases. Used on its own, it is more of a background modulator (oily skin). Good, fast effectiveness in acne requires its combination with, at the very minimum, a keratolytic like salicylic acid.
 Effect of a topical erythromycin-zinc formulation on sebum delivery. Evaluation by combined photometric-multi-step samplings with Sebutape. Pierard GE and Pierard-Franchimont C, Clinical and Experimental Dermatology, 18(5):410-413. 1993.
 Inhibition of 5α-réductase activity in human skin by Zinc and azelaic acid. Stramatiadis D et al, British Journal of Dermatology,119(5): 627-632. 1988.
 Protective effect of Zinc on keratinocyte Activation markers induced by interferon or nickel. Gueniche A, Acta Derm Venereol,75(1): 19-23. 1995.
 Antioxidant-like properties of Zinc In Activated Andothelial Cells. Hennig B and McClain GJ, Journal of the American College of Nutrition, 18(2):152–158. 1999.
 Zinc in wound healing : theoretical, experimental and clinical aspects. Lansdown ABG et al, Wound rep reg, 15(1):2-16. 2007.
 In vitro modulation of keratinocyte wound healing integrins by zinc, copper and manganese. Tenaud I et al, British Journal of Dermatology, 140,(1):26-34. 1999.