Riehl Melanosis Clinical Presentation

Possible subtle signs of a preceding dermatitis include erythema, edema, and pruritus. Such symptoms are generally mild, if present.

Many cases are preceded by mild erythema, edema, and pruritus,^[2] followed by a diffuse-to-reticulated pattern of hyperpigmentation. The pigmentation varies dependent upon the causal agent and can be brown, slate-gray, gray-brown, red-brown, or blue-brown.^{[2, 4, 10]}

The site of pigmented contact dermatitis also depends on the allergen responsible. Pigmented cosmetic dermatitis more commonly involves the face, whereas pigmented contact dermatitis due to textiles more often involves the anterior thighs or the axilla, with sparing of the axillary vault.^[4] Additionally, hyperpigmentation is most pronounced in individuals with darker complexions.

UV exposure may contribute to the hyperpigmentation in select cases, which is supported by the fact that some of the chemicals implicated are known photosensitizers, and, in these cases, the pigmentation appears to be most pronounced in sun-exposed areas.^{[2, 4]}

A variety of contact allergens have been implicated in pigmented contact dermatitis, as described below.^{[3, 4, 10]} Although the majority of cases occur because of direct contact with these allergens, a few cases secondary to contact with airborne allergens have been described.^{[4, 11, 12]}

• Textile allergens

  • Tinopal CH3566 - Optical whitener in washing powder
  • Napthol AS - Coupling agent for azo dyes
  • Biocheck 60 - Pesticide for textiles
  • PPP-HB - Textile finish
  • Mercury compounds - Bactericides
  • Formaldehyde - Preservative
  • Azo dyes - Dye^[13]
  • Disperse Blue 106 - Dye
  • Disperse Blue 124 - Dye
  • CI Blue 19 (Brilliant Blue) - Dye
  • Rubber components
• Cosmetic allergens^[14]

  • D&C Red 31 - Pigment
  • Brilliant Lake Red R - Pigment^{[15, 16]}
  • D&C Yellow No. 11 and 10 - Pigment
  • PAN (phenyl-azo-2-napthol) - Impurity in azo pigments
  • Chromium hydroxide - Pigment
  • Carbanilides (trichlorocarbanilide and Irgasan CF3) - Bactericidal
  • Aniline dyes - Pigment
  • Hair dyes
  • Ricinoleic acid (castor oil acid) - Bactericide (deodorants, lipstick, military camouflage)^[17]
  • Kumkum (red) - Cosmetic powder and liquid (Hindu women)^[18]
  • Fragrances
• Fragrance allergens

  • Jasmine absolute
  • Benzyl salicylate
  • Hydroxycitronellal
  • Ylang-ylang oil
  • Cinnamic alcohol
  • Musk ambrette^{[11, 19]}
  • Cananga oil
  • Sandalwood oil
  • Synthetic sandalwood (containing bornyl methoxy cyclohexanol)
  • Geraniol oil
  • Eugenol
  • Isoeugenol
  • Balsam of Peru
  • Lavender oil
  • Lemon oil^{[20, 21]}
  • Methoxycitronellal
  • Benzyl alcohol
  • Cinnamic derivatives
• Miscellaneous allergens

  • Chromate (K dichromate) - Leather, soaps
  • Nickel/nickel sulfate - Component metal products and jewelry
  • PTBPFR (paratertiary butyl-phenol formaldehyde resin) - Neoprene adhesive in leather products^[22]
  • Plathymenia foliosa - Wood dust^[12]
  • Minoxidil 5% - Topical vasodilator for hair loss treatment^[23]

Cases of pigmented contact dermatitis have been reported in the Indian literature, and the most common allergen to be implicated is kumkum, a colored cosmetic used by Hindu women that is applied most often to the central forehead and along the hair line.^{[4, 18]} Only commercially available red kumkum can sensitize and cause pigmented contact dermatitis. Components of kumkum include azo dyes, coal tar dyes, toludine red, erythrosine, lithal red calcium salt, fragrances, tumeric powder, groundnut oil, tragacanth gum, Cananga oil, and parabens.^[4]

In addition to contact allergens, a Riehl melanosis–like eruption has been reported in Japanese women with Sjögren syndrome related to the development of anti-SSA (Ro) antibodies. The lesions are most pronounced on sun-exposed areas, primarily on the face, and the pigmentation typically resolves with the institution of ultraviolet protection. One hypothesis is that ultraviolet radiation induces expression of the SSA antigen on keratinocytes, which then becomes the target of circulating anti-SSA antibodies, resulting in an interface dermatitis and associated pigment incontinence.^[24]