Bleaching Agents: Hydroquinone is the most commonly used agent for "bleaching" brown marks, liver spots, melasma, etc. Acting to block the formation of the skin pigment melanin, hydroquinone's bleaching activity is reversible, that is, the pigment returns when the hydroquinone is discontinued. Kojic acid, extracted from mushrooms, is a slighly less effective agent. Either may be compounded with AHA's. As with any bleaching agent, aggressive exfoliation and sun protection are necessary for good results. Either agent may produce redness and irritation, especially with prolonged use. Arbutin, extracted from bearberries (licorice), also is an inhibitor of of melanin production, and is often used in skin care products as a soothing agent. 

Antioxidants: The ability of the body to turn nutrients into energy involves Oxidation. in which nutrients are "burned" in a controlled manner to provided energy for growth and repair. An inevitable result of this process is the production of free radicals. Free radicals may also be produced by processes other than oxidation, most notably from ionizing solar radiation, including UVA and UVB.

 

A free radical is an atom or molecule containing an unpaired electron. Elevated to an excited state by some energetic reaction, the unpaired electron will seek to attain a lower energy state by pairing up with another electron or electron rich molecule, as with 2 highly reactive free oxygen atoms pairing up to form the stable O2 molecule. The most significant free radicals in biological systems are those involving oxygen, such as the superoxide (HO2) and hydroxyl (OH) radicals, produced during normal cellular respiration.

 

By providing an electron, antioxidants may convert the free radical to a non-radical species, or to a more stable radical form. The pigment Melanin is an example of a stable radical form, where highly excited electrons are "shared" throughout the aromatic structure of the macromolecule, dissipating the electronic energy as heat. Another example of stable radical forming compounds are the spin trap compounds (see below). Dioxygen (O2) itself is a free radical (actually a diradical).

 

Free radicals play an indispensable role in normal biological processes, but these extremely reactive molecules can cause damage to normal cellular processes and structure, and are a key contributor to the aging process. To defend against damage from free radicals produced in the normal course of cellular function, biological systems have evolved Antioxidants.

 

Biologic antioxidant systems include:

 

Antioxidant enzymes such as superoxide dismutase, catalase, peroxidase

dietary antioxidants such as the tocopherols, carotenes, ascorbic acid, alpha-lipoic acid, glutathione, resveratrol, polydatin, etc.

"solid state" antioxidants such as melanin

DNA repair systems

Antioxidants are often incorporated into skin care products to protect the skin from free radical damage produced by normal aging, pollution, and UV radiation from sun exposure. Many of these antioxidants are available as dietary supplements, or "nutraceuticals", and have been demonstrated to have a plethora of beneficial effects, at least in the laboratory. Their role as topical agents is less well documented.