environmental exposure

What Explains the Brown Discoloration on the Soles of a 7-Year-Old Boy?

Sarah R. Boggs, MD

A 7-year old boy presented with a 1-day history of a bruise-like discoloration of the soles of both feet. The discoloration was first noticed after he had taken a bath; his mother initially thought it was dirt but became concerned when it did not scrub off. The parents were very worried and came to the office expecting that their son would need a full examination and laboratory workup.

At presentation, the child denied any pain, itching, or swelling in his feet. He was able to walk and run normally, and his daily activities had not been affected. He did not remember stepping in anything that could have gotten on his feet, and he did not recall any trauma to his feet. His mother and father insisted that he is never without shoes unless he is inside the house. The family had been camping recently, but the boy had had no other exposures, and no one else in the home had similar findings.

The child did not have any other rash, bleeding, or bruising. He and his parents denied any weight loss, muscle aches, joint swelling, night sweats, cough, fevers, or decrease in appetite or activity in the boy. He reported having occasional headaches with no concerning features, which his mother attributed to not wearing his glasses at school.

Findings of a complete physical examination were normal, including cardiovascular, chest, abdominal, and neurologic evaluation, with the exception of macular brown patches on the plantar surfaces of both feet, sparing the arches. The discolored patches ranged from 0.5 to 1.5 cm in diameter and were nontender and nonblanching, with no change in skin texture and no edema or warmth.

What is causing these brown patches?

A. Henoch-Schönlein purpura
B. Subcutaneous hematoma
C. Plant or chemical exposure
D. Kawasaki disease

(Answer and discussion on next page)

Answer: C, plant or chemical exposure

The discoloration on the boy’s feet was suspected to be an external staining, perhaps related to a plant or chemical exposure. The child’s parents were encouraged to go home and examine the house and yard for anything that could have caused the brown stains on his feet.

The parents called back the next day and reported that 2 days before they noticed the discoloration, their son had visited his grandfather’s house, where he had been shelling black walnuts in the garage and walking around in his socks. They examined the socks he had worn that day, and the pattern of discoloration on the boy’s feet was exactly replicated on the socks.

The black walnut tree, Juglans nigra, is native to the central and eastern areas of the United States. Its wood is prized for use in quality furniture, and its nuts are found in many baked goods and touted as a health food that contains antioxidants and ω-3 fatty acids. The husks of the walnut contain an organic compound called juglone, or 5-hydroxy-1,4-naphthoquinone, with the molecular formula C10H6O3.1 Juglone gives the walnut stain its distinctive color.

Historically, juglone has been used as a dye for hair and skin. It is a semipermanent dye that is similar to henna, and it stains the skin with no involvement of the melanocytes.2 It still is used today in some hair dyes and self-tanners, with the carbonyl group of the juglone molecule interacting with the amidogen radical, NH2, in keratin to form a chromophore that reflects a reddish brown color.3 The color change typically lasts 1 to 4 weeks, depending on the intensity of the exposure.

Our patient had a typical manifestation of black walnut husk exposure. However, there are rare reports of more significant reactions, including a report of a bullous reaction on a woman’s hands after she had shelled more than 30 pounds of walnuts.2 Patch testing confirmed a true allergic dermatitis in the woman. In another report, a baker making walnut cakes experienced severe contact dermatitis over the course of months. After a battery of allergen tests, his only positive result was a wheal-and-flare reaction to a skin prick test for walnut.4 Neri and colleagues reported the case of 2 children with acute irritant dermatitis with lamellar desquamation after having thrown walnut shells at each other.3

Reactions to plant exposures can be difficult to sort out. This case reflects the importance of taking a thorough history, which sometimes is gathered over a period of days and not simply during the few minutes allotted for an office visit. In the absence of any other concerning systemic findings, this case also highlights the appropriateness of reassuring parents while taking a watch-and-see approach rather than immediately ordering a battery of tests that are not indicated. n

Sarah R. Boggs, MD, is an assistant professor in the Department of Pediatrics, Division of General Pediatrics, at the University of Virginia in Charlottesville, Virginia.


1. Compound summary for CID 3806: juglone. PubChem Open Chemistry Database. National Center for Biotechnology Information, National Library of Medicine. http://pubchem.ncbi.nlm.nih.gov//compound/3806. Accessed January 12, 2015.

2. Bonamonte D, Foti C, Angelini G. Hyperpigmentation and contact dermatitis due to Juglans regia. Contact Dermatitis. 2001;44(2):102-103.

3. Neri I, Bianchi F, Giacomini F, Patrizi A. Acute irritant contact dermatitis due to Juglans regia. Contact Dermatitis. 2006;55(1):62-63.

4. Mendonca C, Madan V, Austin S, Beck MH. Occupational contact urticarial from walnut associated hand eczema. Contact Dermatitis. 2005;53(3):