Over-the-Counter Topical Skincare Products: A Review of the Literature

AHAs acids also are the agents used in chemical peels. Although physicians can use high concentrations of AHAs, OTC products must have less than a 10% concentration.

AHAs work by thinning the stratum corneum and speeding up normal skin exfoliation and regeneration.¹³ A 1996 study found that a 25% AHA lotion produced significant reversal in markers of photoaging. The AHA treatment caused the epidermis to thicken, and papillary dermal changes included increased thickness, increased acid mucopolysaccharide, increased density of collagen, and improved quality of elastic fibers.¹⁴ Also, AHAs can be effective even at the lower concentrations present in OTC formulations. A double-blind clinical trial evaluating 8% glycolic acid and 8% L-lactic acid creams found that both creams significantly improved the severity of photodamaged skin when used for a 22-week period.¹⁵

More commonly known as vitamin C, this topical has been shown to produce many beneficial effects supposedly due to its antioxidant properties. However, it must be kept in airtight, darkened bottles to prevent oxidation and inactivity.

Three in vivo studies have shown that ascorbic acid can promote type I and type III collagen synthesis when applied topically.^16-18 More recent studies have shown that topical ascorbic acid also can provide photoprotection against both UVA and UVB rays.^19,20 Finally, topical ascorbic acid has been shown to have an anti-inflammatory function because of its ability to suppress tumor necrosis factor α-induced nuclear factor KB activation.²¹ Although these studies have shown various remarkable effects of vitamin C on the skin, they were limited by relatively small samples sizes.

The lipid-soluble antioxidant vitamin E has been shown to have several beneficial effects when used topically. Its most biologically active form, α-tocopherol, has been shown to reduce and prevent sunburn, neutralize free radicals, and act as a humectant. ²² Recently, several studies have shown that vitamin E has a synergistic relationship with vitamin C. When the two topicals are applied simultaneously, they seem to have a strong protective effect against UV radiation when evaluated in vivo in humans. This phenomenon seems to be connected to the role of vitamin C in the regeneration of oxidized vitamin E.²³ Although vitamin E has been shown in in vitro studies to be involved in collagen and elastin breakdown through its effect on matrix metalloproteinases, no studies have definitively shown that vitamin E improves photoaged skin clinically.

α-Lipoic acid (ALA) is an essential cofactor of the mitochondrial multi-enzyme complex and therefore plays an important role in energy metabolism. Topically, ALA has anti-inflammatory properties and acts as an exfoliant. In a study of 5% ALA applied topically for 12 weeks, it was shown to reduce skin roughness and fine wrinkles.²⁴ However, ALA has not been definitively shown to protect against UV-induced erythema.

Nicotinamide or niacinamide is a potent antioxidant and is the amide form of nicotinic acid, which is vitamin B3 or niacin. Topical niacinamide improves the lipid barrier present in the stratum corneum and therefore reduces transepidermal water loss. Also, several studies have shown that topical niacinamide can significantly reduce fine lines and wrinkles.²⁵ It also has been shown to help eliminate hyperpigmented spots, most likely due to its role as an inhibitor of melanosome transfer.²⁵ Finally, recent studies have shown that niacinamide also can improve skin elasticity and reduce sallowness.²⁶

Glucosamine and its more stable derivative N-acetyl glucosamine (NAG) are amino monosaccharides with essential biochemical functions. Glucosmine and NAG also act as substrate precursors for the biosynthesis of polymers such as the glycosaminoglycan hyaluronic acid and in the production of proteoglycans. Topical glucosamine has been shown to accelerate wound healing and improve skin hydration when taken orally. It also may reduce skin wrinkles when used in conjunction with niacinamide.²⁷ Because of its stimulation of hyaluronic acid synthesis, glucosamine acts as an inhibitor of tyrosinase activation and therefore inhibits melanin production. Because of this role, topical glucosamine has been used to reduce hyperpigmentation.²⁸ Also, the combination of topical niacinamide and NAG has been shown to have a synergistic effect in reducing hyperpigmentation.²⁹

Grape Compounds: Resveratrol, Flavenoids, and
Grape Seed Extract
Resveratrol
This compound is a stilbenoid, a type of natural phenol produced by plants when attacked by pathogens. Resveratrol is most commonly found in the skin of red grapes and certain other fruits. The effects of resveratrol are currently a topic of numerous animal and human studies. Recently, in vitro and in vivo studies in animal models have found that topical resveratrol inhibited UV-induced carcinogenesis and photodamage.³⁰ It can be hypothesized that topical resveratrol also may have an effect on the visible signs of photoaging, which also is caused by exposure to UV radiation.

Flavenoids
A 2011 in vitro study showed that several antioxidant polyphenolic fractions from grapes protected human keratinocytes against UV-induced oxidative damage. The highest protective effect was for fractions rich in procyanidin oligomers and gallate esters.³¹