Continuing Education Activity
Riehl melanosis (RM), commonly called pigmented contact dermatitis, is considered an acquired form of allergic contact dermatitis, typically to fragrance and other ingredients of cosmetic products. Although it is considered as a dermatitis, it presents clinically with hyperpigmentation over the face and shows pigment incontinence with minimal eczematous changes on histology. The condition is more commonly seen in dark-skinned people, causing an important psychosocial impact. This activity reviews the evaluation and treatment of Riehl melanosis and highlights the role of the interprofessional team in the care of patients with this condition.
- Summarize the epidemiology of Riehl melanosis.
- Identify the evaluation of a patient with suspected Riehl melanosis.
- Review the current management options available for Riehl melanosis.
- Explain the importance of improving care coordination among the interprofessional team to improve outcomes for patients affected by Riehl melanosis.
Facial melanoses affecting the face and neck region are of considerable concern to darker-skinned people. Although many facial melanoses, such as melasma, are well defined clinically, rendering them easy to diagnose, others have overlapping clinical morphology as well as histopathology. Riehl melanosis (RM), commonly considered as a pigmented contact dermatitis (PCD), is one such condition with diverse yet overlapping clinical features with other facial melanoses such as ashy dermatosis and lichen planus pigmentosus.
RM is best defined as an acquired low-grade allergic contact dermatitis to fragrance and other cosmetic products that presents with abnormal hyperpigmentation involving the face and neck regions. The disorder is known to predominantly affect patients of Asian descent.
Historical Aspects of Nosology of Riehl Melanosis
During the first world war, Riehl first identified several patients of both genders with striking dark brown to grayish-brown pigmentation on the forehead, temporal, and zygomatic regions of the face. The involved skin was mildly indurated with a rough texture and appeared to mildly scaly without any erythema or atrophy. The pigmentation was diffuse and uniform but without well-defined margins. It extended to the ears and neck, with gradual fading off towards the chest as small discreet pigmented follicular-based macules. Other body parts like the axillae, arms, and forearms, submammary and umbilical regions also showed similar pigmentation, but it was much lighter than the face. Riehl was uncertain about the etiology, but he suggested wartime food substitutes, mainly poor-quality flour, as being contributing factors. The condition seemed to have disappeared, with no cases reported towards the end of the war.
Later, similar cases were described from different centers. Hoffmann and Habermann emphasized that local chemical irritation due to the use of certain oils and hydrocarbons were responsible for melanosis similar to Riehl melanosis and labeled it 'melanodermatitis toxica.' However, this entity was not accepted by Riehl. The term "Riehl melanosis" became popular in the period between the two world wars for facial melanosis caused by external chemical agents. During the second world war (1945-1948), 165 new cases of suspected RM were diagnosed in Vienna with a female predominance. This condition disappeared again with the end of the war. Since then, RM was reported from many centers across the globe, especially from France and Argentina.
The inflammatory component of the early phase of RM was strongly suggested by Miescher and was confirmed on histology in 200 cases by Joulia et al. in 1950.
The etiology of RM was unknown until the late 1940s and 1950s when two studies from Argentina by Pierin et al. and Puente et al. attributed facial pigmentation similar to RM to cosmetic ingredients, typically aniline dye (orange II) found in facial powder. Positive patch tests to the dye were supported by the disappearance of early inflammation and progressive reduction in pigmentation on discontinuing the use of the facial powder.
In 1970, the term "pigmented contact dermatitis" was coined by Osmundsen, a Danish dermatologist who documented several cases of peculiar facial hyperpigmentation in Copenhagen. Investigation revealed that the hyperpigmentation was the result of contact dermatitis to an optical whitener, tinopal CH 3566, in washing powder.
Subsequently, in 1973, the term pigmented cosmetic contact dermatitis was introduced by Nakayama, a Japanese dermatologist, for cases that were ascribed to cosmetic contact allergens especially the pigment brilliant lake red r.
To date, the etiology of RM is still controversial, although the majority of experts consider it synonymous with PCD of the face. However, a recent global consensus statement emphasized that finely reticulated hyperpigmentation on the face and neck region should be labeled “pigmented contact dermatitis” rather than RM if its appearance is preceded by contact allergy. If the etiology is uncertain, the term RM should be used.
The etiology of Riehl melanosis remains controversial, whether it is associated with intrinsic or extrinsic factors. The majority of cases occur clearly because of exogenous factors, leading the authors, as described below, to label it a contact dermatitis. It usually results from direct contact with several allergens. However, a few cases secondary to contact with airborne allergens have been also described. Ultraviolet (UV) exposure may play a role in some PCD since hyperpigmentation is often photo-localized, and some of the causative chemicals are known photosensitizers.
The common cosmetics allergens are as follow:
- Aniline dyes
- Red and yellow pigments
- Brilliant lake red r: widely used in cheek rouges and lipsticks until 1976
- Chromium hydroxide: pigment
- Carbanilides (photosensitizer): bactericidal agent
- Ricinoleic acid: bactericidal agent
- Hair dyes
- Kumkum: a red-colored vermillion powder that adorns the forehead at the central parting line of the hair as a cultural symbol of their married status
The common perfume allergens are as follows:
- Geraniol oil
- Lemon oil (photosensitizer allergen)
- Musk ambrette (photosensitizer and airborne allergen)
- Ylang-ylang oil
- Jasmine absolute
- Lavender oil
The common textile allergens are as follows:
- Tinopal CH3566: Optical whitener in washing powder
- Naphthol AS: coupling agent for azo dyes
- PPP-HB: textile finish
- Mercury compounds: bactericides
- Formaldehyde: preservative
- Azo dyes: dye
- Rubber components
The common occupational allergens are as follows:
- Coal tar
- Mineral oil
Other allergens had also been described like Plathymenia foliosa (wood dust; airborne allergen), minoxidil 5%, chromate (leather, soap), and nickel sulfate (metal product).
Nevertheless, a few cases due to endogenous factors have been also described such as nutritional effects suggested by Riehl, toxic factors, neurovegetative lability, and digestive disorders. Additionally, a Riehl melanosis–like eruption had been reported in Japanese women as a cutaneous manifestation of Sjögren syndrome caused by the development of anti-SSA (Ro) antibodies. Pigmentation gradually disappeared when the patient avoided sun exposure. Cosmetics and detergents had not been interrupted.
Repeated contact with low concentrations of these allergens explains why they do not provoke an eczematous reaction in the middle of the spinous cell but instead, their accumulation induces type IV allergic cytolytic reactions in the basal layer.
The incidence of RM is not known. Riehl melanosis is more common in darkly pigmented races. Young to middle-aged women are the most concerned group. However, men and children could also be affected by PCD. A large proportion of reports are from Japan, but cases have also been described in Europe, South America, India, and South Africa.
Most biopsy results have shown interface dermatitis. Riehl melanosis presents, in early lesions, with vacuolar basal layer degeneration, perivascular or band-like dermal lymphohistiocytic infiltrate, and dermal pigmentary incontinence. At a later stage, histologic examination shows rather upper dermal melanophage infiltration. The direct immunofluorescence study is negative.
History and Physical
Riehl melanosis typically presents as patchy to diffuse pigmentation, often with a slightly scaly skin surface and satellite pigmented follicular-based macules. The reticular pattern is often observed at the center of the pigmented areas.
Some patients complain of erythema, edema, and pruritus preceding the occurrence of the pigmentation. This inflammatory phase suggests the onset as an ordinary contact dermatitis caused by allergens when they came into contact with the skin.
Different shades of brown could be encountered, depending on the severity of dermatitis, skin type, and causal agents (black, purple, blue-black, pale brown, or gray-brown).
Sites of involvement are variable, depending on the allergen responsible. Pigmented cosmetic dermatitis involves usually the face (forehead, zygomatic and temple regions), whereas textile contact dermatitis more often involves axillary borders; sparing the vault. When the allergens implicated are photosensitizers, the pigmentation is more pronounced in sun-exposed areas.
Dermoscopy may represent a non-invasive aid to the clinical diagnosis of Riehl melanosis. The most common observed findings are pseudonetworks, gray dots or granules, and telangiectatic vessels.
Reflectance confocal microscopy of biopsies correlates with the conventional histopathologic examination and may show pigment incontinence, mildly refractive cells corresponding to infiltrated lymphocytes, dilated vessels, and features of basal layer liquefaction including obscured papillary rims, total or partial obliteration of the ring-like structures around the dermal papillae.
Patch testing is recommended in diagnosing RM. Closed patch testing should be performed with standard series, cosmetic series, fragrance series, and patient’s products. If photoallergy is suspected, photo-patch testing should be carried out. Patch test sites may show papule, vesicle, or brown pigment. Given the low concentration of the allergen in cosmetic and fragrance series, repeated open application test (ROAT) are needed if closed patch testing is negative or equivocal. If ROAT performed on the flexor forearm skin is equivocal, the patient’s product could be applied to the face or other affected areas.
Skin biopsy is not required unless there is an atypical clinical presentation.
Treatment / Management
There is no standardized treatment for Riehl melanosis. Several therapeutic options have been attempted, either individually or in combinations, with variable results in RM.
Treatment modalities for RM are as follows:
- Removal of causal agents to prevent further disease progression and relapse
- Cosmetic camouflage makeup
- Vigilant sun-protection
- Topical agents including hydroquinone, topical corticosteroids, retinoids, vitamin C, azelaic acid, with or without the addition of light to medium chemical peels (trichloroacetic acid, glycolic acid)
- Light-based therapies such as intense pulsed-light therapy and low-fluence Q-switched Nd: YAG lasers (QSNY).
A recent study showing the higher effectiveness of mid-fluence QSNY 1064-nm laser in targetting the deep pigmentation of RM has also been conducted.
A combination of therapies should be considered for recalcitrant forms. Recently, a significant improvement of RM had been reported with a triple combination of salicylic acid peels, oral glycyrrhizin compound, and vitamin C.
Another study used a combination of therapies to include low-fluence, 1064-nm, Q-switched Nd: YAG laser, hydroquinone cream, and oral tranexamic acid, with the majority of patients experiencing significant improvement.
Various diseases can mimic Riehl melanosis.
Disorders Related to RM 
- Lichen planus pigmentosus presents as a diffuse slate-gray to black pigmentation affecting overexposed areas and flexures. It is generally associated with classical lichen planus.
- Poikiloderma of Civatte manifests clinically as a dark pigmentation with a reticulate distribution, telangiectasia, and atrophy, located on the sides of the neck. Photodynamic substances in cosmetics may play an important role.
- Erythromelanosis follicularis of the face and neck is characterized by follicular-based papules surrounded by reddish-brown pigmentation and causing hair loss. Etiology is unknown.
- Erythrose peribuccale pigmentaire of Brocq typically appears as a brown-red pigmentation around the mouth, sparing the vermillion border. It may result from photodynamic molecules present in cosmetics.
- Linea fusca is characterized by an arciform brown-yellow pigmentation near the hair implantation affecting the forehead and temporal areas. Other dark patches can be noticed all over the face. This disorder is likely caused by the use of cosmetics and hat ribbons, but it might also reveal encephalitis, central nervous tumors, and neurosyphilis.
- Erythema dyschromicum perstans manifests as multiple asymptomatic, gradually enlarging hyperpigmented macules with a raised erythematous border. Lesions sometimes become coalescing, covering extensive areas of the face, trunk, and limbs. Ashy dermatosis is characterized by similar lesions to erythema dyschromicum perstans but without erythematous borders. Etiology is controversial.
Histologically, these diseases are marked by a lichenoid reaction, added to the other characteristic findings.
Other Differential Diagnosis
- Drug-induced melanodermas: Several classes of drugs are incriminated: tetracyclines, salicylamides, sulfonamides, chlorpromazine, chlorothiazides, some oral antidiabetics, phenothiazines, minocycline, antimalarials, psychotropic drugs, chemotherapeutic agents, and psoralens
- Nevus of Ota and Hory nevus
- Addison disease
- Exogenous ochronosis
- Postinflammatory hyperpigmentation
- Idiopathic eruptive macular pigmentation
- Allergic contact dermatitis
- Irritant dermatitis
- Riehl melanosis is not a life-threatening disorder but has an increased risk of psychosocial effects.
- Despite the tendency to lighten over time, pigmentation may persist for months or even years.
- Satisfactory treatments are presently lacking.
- Resistant cases or relapses of RM occur often and are certain if the avoidance of precipitating factors is not strictly heeded.
- Cosmetic disfigurement
- Lack of self-esteem
- Anxiety and depression
- Social stigma
- Poor quality of life
- Side effects of treatment
Deterrence and Patient Education
Patients shall be educated about the importance of these general instructions:
- Avoidance of the causal allergen is mandatory. Its removal results in gradual improvement.
- Consider the use of allergen-free skin-care products.
- Sun avoidance is recommended. This entails using broad-spectrum sunscreens, appropriate clothes, and avoiding peak hours of sunlight.
- Treatment should not be discontinued promptly since several months are needed before the effect becomes apparent.
Enhancing Healthcare Team Outcomes
Currently, Riehl melanosis is considered as a non-eczematous allergic contact dermatitis to fragrance, cosmetics, and sometimes occupational agents. It is specially marked by a reticulate gray-brown to black pigmentation involving the face and neck, interface dermatitis, and pigment incontinence. Hence, the diagnosis is best reached with an interprofessional team including dermatologists, pathologists, pharmacists, and occupational clinicians. The goal of treating patients is aesthetic. Fortunately, RM may resolve gradually on its own when the trigger factors are removed. Hence, healthcare workers including primary care clinicians, pharmacists, dermatologists, and nurse practitioners, should educate the patient on avoiding the suspected allergen and sun exposure. The outcomes for most patients are unpredictable. The condition is known to cause psychosocial impact, and hence a mental health counselor should be consulted.