bubble_chart Overview

Occupational melanosis, also known as tar melanosis or melanodermatitis toxica lichenoides, is now more appropriately referred to as occupational melanosis.

bubble_chart Etiology

Occupational melanosis is a chronic skin inflammation caused by prolonged exposure of workers to asphalt, coal tar, petroleum products, or long-term inhalation of volatile substances from these materials, ultimately leading to skin pigmentation.

Asphalt contains various substances such as phenols and naphthalene that irritate the skin, causing dermatitis. The photosensitive substances like acridine and anthracene in asphalt make the skin sensitive to light, leading to solar dermatitis. This is especially common among workers handling, loading, or transporting asphalt. Within hours, skin redness, swelling, pain, blisters, eyelid swelling, conjunctival and corneal congestion, photophobia, and tearing can occur on the face, neck, back, and limbs. Some may also experience respiratory irritation, dizziness, nausea, fatigue, and other symptoms. Repeated acute asphalt dermatitis or long-term exposure to asphalt can lead to chronic dermatitis, characterized by dry skin, lichenification, and secondary pigmentation. Asphalt-induced skin melanosis is believed to be caused by substances in asphalt that affect melanin metabolism. Wart-like skin lesions may also occur, and in rare cases, cancerous changes.

Coal tar: Like asphalt, coal tar causes photosensitivity, with exposed areas rapidly becoming red, swollen, and painful, sometimes even forming blisters. Some patients may experience headache, nausea, fever, and other systemic symptoms. Long-term exposure to coal tar can lead to pigmentation known as tar melanosis, or lichenoid toxic melanodermatitis (Melanodermutitis toxica lichenoides). This is thought to be due to substances in coal tar that stimulate tyrosinase or increase the secretion of melanocyte-stimulating hormones from the pituitary gland. Affected areas show reticular pigmented spots, grade I capillary dilation, shiny skin, excessive sweating, and numerous black lichenoid follicular papules, especially on the forearms.

Prolonged hand contact with petroleum can cause dry, rough skin, making it prone to rhagades, which worsen in winter. Carbon black from gasoline can also cause pigmentation.

The common feature of occupational melanosis is a clear history of occupational exposure, typically occurring in exposed areas (face, forearms, neck, and limbs). Before the onset, there may be grade I cutaneous pruritus and edematous erythema. Repeated episodes can lead to diffuse or reticular pigmented spots, ranging from light to dark brown, accompanied by capillary dilation, acne-like lesions, black lichenoid follicular papules, and grade I skin atrophy.

This condition is more common in male workers, often occurring in winter, and is frequently accompanied by systemic symptoms such as headache, dizziness, fatigue, and loss of appetite. The pathological changes are similar to those of Riehl's melanosis.

bubble_chart Treatment Measures

(1) During the use and production of the aforementioned substances, improve operational methods to minimize contact opportunities. Install ventilation, exhaust, and dust collection equipment to reduce the concentration of smoke and dust in the workshop. When handling asphalt, take necessary protective measures, preferably during nighttime and overcast days.

(2) Strengthen personal protection by wearing work clothes, work caps, masks, and gloves, and apply light-protective agents to exposed skin areas.

(3) Those with severe dermatitis should cease contact and avoid sun exposure. For those with obvious rash exudation and redness, a 3% boric acid solution can be used for wet compresses, and zinc oxide oil can be applied externally. Those with severe systemic symptoms may take corticosteroids and antihistamines, and intravenous drip may be administered if necessary. Vitamin C, which inhibits melanocyte production, can be given in large doses intravenously, such as 1g of Vitamin C added to glucose solution for injection, once daily for a 10-day course. Multivitamin therapy can also be combined.

For local treatment of severe pigmentation, 3% hydroquinone cream or 5% ammoniated mercury ointment can be applied externally.

bubble_chart Differentiation

This disease should be differentiated from Riehl's melanosis, Civatte's poikiloderma, pigmented cosmetic dermatitis, and Addison's disease.

(1) Civatte's poikiloderma: Patchy reticular pigmentation on the face and sides of the neck, with the pigmentation appearing as brownish-red or bronze spots densely clustered in a reticular pattern, interspersed with atrophic white spots and telangiectasia. The rash surface is smooth, occasionally with fine scaling, and there are no subjective symptoms. It is unrelated to seasons or sunlight.

(2) Addison's disease: Characterized by low blood pressure, low blood sugar, and low urinary 17-ketosteroid levels. The pigmentation is bronze-colored, mostly in skin folds. Mucous membranes are affected.

(3) Pigmented cosmetic dermatitis: Occurs in areas of the face where cosmetics are applied, with pigmentation around the eyes, on both sides of the nose, cheeks, or forehead. The borders are clear, appearing as light brown, reddish-brown, or light black, in diffuse patches or a reticular pattern. Some patients may experience grade I cutaneous pruritus.