An increasing number of natural ingredients are being formulated into over-the-counter skin care products. This articles discusses some of the most recent entries and the mechanisms underlying their purported effects
"Natural ingredients are used particularly in cosmeceuticals for treating photodamage, for their ability to reduce UV damage, inhibit inflammation, restore collagen and decrease pigmentation of the skin.
"They provide these effects via mechanisms involving some physiologic function, although it is often difficult to see the link between the active natural ingredient and the physiological function in some relevant, visible fashion," says Dr. Draelos, clinical associate professor of dermatology, Wake Forest University School of Medicine, Winston-Salem, N.C.
Retinoids are naturally occurring derivatives of vitamin A that exert their clinical effects via receptor activation. Retinol is the most biologically active of the natural retinoids. However, at concentrations exceeding 2 percent, it causes irritation and stains the skin yellow.
Therefore, it is not possible to formulate a retinol-containing cosmeceutical product with efficacy comparable to that of a prescription tretinoin preparation.
This formulation challenge has led to the development of a new class of colorless carotenoids. Obtained from compounds found in tomatoes or monocellular algae, the colorless carotenoids differ structurally from the retinoids by having one less double bond.
"They do not stain the skin when used at higher concentrations, are also more photostable than retinol, and will be introduced in new products in 2008," Dr. Draelos tells Dermatology Times.
Antimicrobial peptides represent another new class of natural ingredients that will be introduced into the consumer marketplace and produce their effects via receptor activation. These peptides exert their activity by coating and adhering to the surface of cells.
One hexapeptide has been found to have substantial antimicrobial activity, including the ability to inhibit growth of methicillin-resistant Staphylococcus aureus, Enterococcus faecalis and Escherichia coli. Importantly for dermatology, this hexapeptide has also been shown to decrease growth of Propionibacterium acnes on the skin.
Natural ingredients able to inhibit tyrosinase and cause pigment lightening have been available in over-the-counter (OTC ) products for years, and include arbutin and soy.
Deoxyarbutin is a more recent entry within this category. Introduced in products first marketed in 2006, deoxyarbutin is a potent, naturally occurring hydroquinone analogue that is a chemical modification of arbutin, but more stable and less expensive than its parent molecule. In addition, deoxyarbutin inhibits tyrosinase reversibly and does not cause cytotoxic effects, Dr. Draelos explains.
N-acetyl glucosamine is also new. In addition to inhibiting glycosylation of tyrosinase to cause pigment lightening, n-acetyl glucosamine stimulates hyaluronic acid synthesis to increase skin humectancy and reduce wrinkles of dehydration.
Interrupting oxidative damage
Products containing natural ingredients to interrupt oxidative damage represent one of the most proliferating areas in the cosmeceutical marketplace. The ability of these compounds to reduce formation of sunburn cells is used to validate their antioxidant activity and to promote product antioxidant product claims.
"However, because many naturally occurring agents have antioxidant activity, this is also the shadiest area of the natural ingredient category. And while reduction of sunburn cells is a very nice clinical test, we have to wonder how well it correlates with oxidative damage reduction. After all, the purpose of antioxidants is to prevent skin damage from appearing many decades later," she says.
Feverfew is the most introduced natural ingredient with antioxidant activity, while green tea polyphenols, which contain a variety of catechins, are among the most important within this category.
"Polyphenols are quite promising for their antioxidant effect. In addition, they have been shown in human studies to increase remaining Langerhans cells, indicating they also decreased UV immunosuppression," Dr. Draelos says.