Pigmentary Disorders, Photodermatoses, and Skin of Color
Pigment, light, and skin type
Pigmentary disorders are approached through melanocyte number and function, and photodermatoses through timing after exposure and action spectrum.
Concepts to master
- Vitiligo: depigmented macules with a sharply defined border; Wood lamp accentuates. Distinguish from postinflammatory hypopigmentation and pityriasis versicolor.
- Melasma: symmetric hyperpigmentation of sun-exposed face; worsened by ultraviolet and visible light, pregnancy, and hormonal therapy.
- Postinflammatory hyperpigmentation: common in darker skin types; treat the underlying inflammation first.
- Photodermatoses: polymorphous light eruption (delayed, hours to days, itchy papules on sun-exposed skin), solar urticaria (immediate), chronic actinic dermatitis (persistent, severe, often in older men), and photoallergic contact dermatitis (fragrances, sunscreens).
- Skin of color: keloids, acne keloidalis nuchae, traction alopecia, and pigmentary alteration after inflammation are common. Inflammatory disease may appear violaceous or gray rather than red.
Traps
Do not confuse vitiligo with chemical leukoderma or piebaldism (which is present at birth with a white forelock). Melasma is not just "sun damage" - visible light and hormones matter, so broad-spectrum tinted sunscreen is part of therapy. In darker skin, erythema is often invisible, so rely on texture, warmth, and patient report.
Rule of thumb
For photodermatoses, the time to onset after sun exposure is the fastest discriminator: immediate suggests solar urticaria; hours to a day suggests polymorphous light eruption; persistent and severe suggests chronic actinic dermatitis.