Hyperpigmentation

The overproduction of melanin is a complex process driven by UV radiation, hormonal fluctuations, and inflammation.

Pathophysiology of Melanogenesis

Melanin is produced by melanocytes in the basal layer of the epidermis. The primary enzyme responsible for this synthesis is tyrosinase, which converts the amino acid tyrosine into DOPA and subsequently into melanin.

Once synthesized, melanin is packaged into organelles called melanosomes, which are then transferred via dendrites to surrounding keratinocytes.

Clinical Subtypes

Post-Inflammatory Hyperpigmentation (PIH): Triggered by cutaneous injury or inflammation (e.g., acne, burns). More prevalent in Fitzpatrick skin types III-VI. Can affect the epidermis or dermis.
Post-Inflammatory Erythema (PIE): Often confused with PIH, PIE represents vascular damage (dilated capillaries) following acne. It is red/purple, not brown, and does not respond to melanin inhibitors.
Melasma: Symmetrical, blotchy hyperpigmentation often occurring on the face. Highly linked to hormonal changes (pregnancy, oral contraceptives) and exacerbated by UV and visible light (blue light) exposure.

Therapeutic Pathways

Effective management requires targeting multiple stages of the melanogenesis pathway simultaneously:

Pathway Target	Mechanism	Key Actives
Tyrosinase Inhibition	Blocks the initial synthesis of melanin by inhibiting the tyrosinase enzyme.	Hydroquinone (gold standard), Kojic Acid, Alpha Arbutin, Vitamin C, Azelaic Acid, Thiamidol.
Melanosome Transfer Inhibition	Prevents the transfer of melanin packets from the melanocyte to the keratinocyte.	Niacinamide (Vitamin B3).
Keratinocyte Turnover	Accelerates the shedding of melanin-laden surface skin cells.	Retinoids (Tretinoin, Retinol), AHAs (Glycolic Acid, Lactic Acid).
Plasminogen Inhibition	Reduces UV-induced melanogenesis and vascular-driven melasma components.	Tranexamic Acid (Topical or Oral).