Tomato Plant-Associated Xanthoderma: Case Report and Review of Exogenous Causes of Yellow Skin

The skin, hair, and nails can all present with yellow discoloration secondary to exogenous etiologies. Xanthoderma, yellow discoloration of the skin, can occur not only from exogenous sources secondary to topical contact with various substances but also from endogenous causes such as diseases from the liver and kidney, or oral medications. A 64-year-old man developed asymptomatic, yellow staining of his distal left forearm, hand, and fingertips. He was not receiving antimalarials, did not have hepatic or renal dysfunction, and had not applied any sunless tanning solutions to his skin. Prior to the appearance of his xanthoderma, he had been tending to a tomato plant in his yard; the yellow staining appeared on the areas of his left upper extremity that had contacted the stems and leaves of the tomato plant. Within two days, the yellow skin discoloration resolved spontaneously after several washings of the affected areas with soap and water. Tomato plants have trichomes that appear as hair-like structures on the stems and produce an oily substance; the trichomes not only produce the scent of the plant, but also provide protection from cold, drought, disease, and pests. Initially, when the oily substance contacts the skin, the skin appears yellow; subsequently, the skin may become black. The skin that has been stained by a tomato plant is referred to as "tomato skin" (TOMASK). In addition to reviewing the etiology of exogenous xanthoderma, this paper also summarizes the causes of exogenous yellow hair and yellow nails. Exogenous yellowing of the skin can result from various topical causes. Common topical etiologies of xanthoderma include not only contact with tomato plants, but also sunless tanning solutions (that contain dihydroxyacetone) and tobacco (that not only causes yellow staining of the white hair on men's upper lip referred to as "smoker's mustache", but also yellow staining of the nail plate and fingertips used to hold the cigarette or cigar). In summary, tomato plant-associated xanthoderma is a benign exogenous etiology of yellow staining of the skin which eventually resolves after several washings of the affected sites with soap and water.