A 24-year-old woman in Norway had been leaving blue stains on her clothes, towels, furniture, and shower for a year when doctors learned that her husband had developed a faint blue tint on his own chest weeks after hers. Swabs from both of them grew the same bacterium, Bacillus cereus. Their newborn's skin showed only normal bacteria.
That family's case, published in Acta Dermato-Venereologica in late 2019, has become a reference point as blue sweat keeps turning up in medical journals. A 17-year-old girl with an intermittently bright-blue arm was described this year in the Journal of Pediatric Health Care, and an 88-year-old man in Brazil had blue sweat and blue-stained nails linked to Pseudomonas stutzeri in an infected leg wound, according to a March report in Cureus. Read together, the reports point to a pattern: the color usually comes from microbes on the skin, and outside factors such as medications or close contact may help them take hold.
