Many topical products claim to reverse the signs of cutaneous photodamage, namely dyspigmentation and rhytid development. To date, the two most studied ingredients for improving the texture, tone, and pigmentation of the skin are topical retinoids and hydroquinone.
All-trans-retinoic acid (tretinoin), a naturally occurring metabolite of retinol, a form of Vitamin A, was the first retinoid to be synthesized, and has been used in topical skin care applications for acne reduction and treatment of photoaging since 1969.2 Several strengths and formulations are commercially available in the US. Clinical studies have demonstrated efficacy of tretinoin, a prescription-strength retinoid, as a topical agent for the treatment of photodamaged skin,3 but the potential for side effects such as dryness, scaling, erythema, itching, burning, and photosensitivity4 may limit patient tolerance and duration of use.
Hydroquinone (1, 4 dihydroxybenzene) has long been used to treat cutaneous hyperpigmentation including melasma, solar and senile lentigines, ephilides, post-inflammatory hyperpigmentation, and other forms of dyschromia. Applied topically, hydroquinone acts as a tyrosine inhibitor to halt a critical step in melanogenesis.5 Despite its effectiveness, hydroquinone has several potential side effects including an irritant, allergic contact dermatitis, and exogenous ochronosis.6 A variety of neoplasms have been reported in rodent studies where the animals received large systemic doses of the medication, but relevance to topical therapy in humans has not been determined.7 Because of these concerns, hydroquinone has been removed from Japanese and European markets. In the US, 2% formulations are available over the counter, while 3% solution and 4% cream or gel require a prescription.
While tretinoin and hydroquinone are among the most commonly prescribed topical agents for treatment of cutaneous photoaging, several barriers to their use exist. Prescription strength hydroquinone and all tretinoin formulations require a physician assessment to obtain a prescription. Annual monitoring of retinoic acid and quarterly monitoring of 4% hydroquinone is the generally accepted protocol for safety and efficacy.
Other retinoids and hydroquinone formulations are available in over the counter cosmetic preparations. These products may be less irritating than their prescription-strength rival,8 however, there are few, if any, clinical studies comparing over the counter versus prescription strength products. The objective of this