Beyond the ink: Marking the skin with henna through ultrasound gel

To evaluate henna as a durable skin marker on various skin tones for sonographic targeting and to identify the shortest duration of henna application needed for practical clinical workflow.

Prospective study applying seven henna lines through ultrasound (US) gel on the forearms of 15 healthy participants equally represented across the validated six-color bar tool. Color bar categories 1-2, 3-4, and 5-6 were designated low, moderate, and high-melanin groups, respectively. Each subsequent line was applied with staining wait-times ranging from 10 to 480 s. Serial photographs were obtained after scrubbing with chlorhexidine every 2-3 days with the number of clearly visible lines assessed by participants, by individual and consensus physician reads, and by band intensity quantification.

Henna could be applied through US gel and the markings were resistant to chlorhexidine scrubbing. Staining wait-times for 60, 120, and 240 s resulted in visible lines for 6, 8, and 10 days (low-melanin), 5, 6, and 8 days (moderate-melanin), and 2, 3, and 4 days (high-melanin). No lines were visible on day 13 for most participants in the low or moderate-melanin groups and on day 6 on most participants in the high-melanin group. The marking intensities decreased more quickly in the moderate-melanin group compared the low-melanin group.

Henna is an effective skin marker that can be applied through US gel where short staining wait-times result in markings lasting several days. To achieve the same durability, staining wait-times are about double for high-melanin skin tones compared to low or moderate-melanin skin tones.