The first step in managing PIH is the treatment of the underlying dermatoses that stimulates pigment production.

At the same time, photoprotection is also critical to prevent further darkening of PIH and to allow depigmenting agents or physical modalities to be safe and effective. Patients should be educated to avoid prolonged direct sun exposure, to use protective clothing and hats, and to apply broad-spectrum sunscreens. Sunscreens containing physical filters that protect from visible light are preferable; however, their use is limited because of their impaired cosmetic effect (skin whitening).

It is important to have in mind that treatments that cause irritation may exacerbate PIH instead of improving it.

Hydroquinone. Hydroquinone remains the main agent used to treat PIH. It blocks the conversion of DOPA (dihydroxyphenylalanine) to tyrosinase. It is also selectively toxic to melanocytes, inhibiting DNA and
RNA synthesis and promoting melanosome degradation. It is commonly used in concentrations from 2% to 4%, but up to 10% may be used. It may be applied alone as a monotherapy, or formulated in combination with other compounds to increase efficacy.³ A popular formulation comprises hydroquinone and a corticosteroid to reduce inflammation, along with tretinoin to reduce the corticosteroid-associated atrophy and to increase keratinocyte turnover and the penetration of hydroquinone.

Adverse events include allergic contact dermatitis, nail discoloration, and hypopigmentation of the surrounding normal skin that has been treated with hydroquinone. Exogenous ochronosis has been associated with long-term use of hydroquinone because it specifically inhibits the enzyme homogentisic acid oxidase locally and may result in the accumulation of this substance on the collagen fibers in tissues where it is applied. Continuous treatment should be limited to 3 to 6 months.

Despite the 2006 US Food and Drug Administration release of the potential carcinogenic effects of hydroquinone (based on oral administration of the drug to rodents),⁴ no reports of skin cancers or internal malignancies is so far associated to topical hydroquinone use.

Mequinol. Mequinol is a derivative of hydroquinone and thought to be less irritating. It is available through prescription in some countries, typically formulated with tretinoin 0.01%. It is published to be effective for solar lentigines⁵ and melasma.⁶ No full paper studies have been published with its use for PIH.

Azelaic Acid. Azelaic acid is a naturally occurring dicarboxylic acid. It inhibits tyrosinase activity.⁷,⁸ Azelaic acid 20% cream improves facial hyperpigmentation⁹ in patients with darker skin and is considered a good option for acne-associated PIH because it improves both conditions.¹⁰ Azelaic acid may cause mild transient irritation and stinging. No leukoderma or exogenous ochronosis are associated with its prolonged use.