With news of more than 70,000 confirmed cases and 1700 deaths from the COVID-19 virus, the importance of handwashing is once again front and center. Using data from a 1978 study on the hygiene of health professionals, this is a map of the most missed areas when washing hands.

This more recent paper contains a short review of various studies of missed areas, most of which conclude that people often forget to wash their fingertips:

In 2008, the WHO designed a handwashing leaflet, making reference to Taylor, who indicated that the fingertips, interdigital areas, thumbs, and wrists are the most commonly missed areas in handwashing. Pan et al. also found that the tips of the nails and the fingertips had the largest amount of residual florescent stains left after handwashing among healthcare workers in Taiwan. The commonly missed areas among medical students in the study conducted by Vanyolos et al. was the first metacarpal, the proximal part of the palm (lateral), the distal phalanges, and the nail beds. In healthcare workers in Škodová et al.’s study, the thumbs and fingertips were the most commonly missed areas. In this study, the most frequently missed area was also the fingertips. However, the medial aspect and back of the hand were the second and third most missed areas, respectively. Moreover, the interdigital area and the front and back of the fingers were the least missed areas, which is in contrast to Taylor’s study.

So wash those fingertips! Here’s the CDC-recommended guide to washing your hands properly.

Wet your hands with clean, running water (warm or cold), turn off the tap, and apply soap. Lather your hands by rubbing them together with the soap. Lather the backs of your hands, between your fingers, and under your nails. Scrub your hands for at least 20 seconds. Need a timer? Hum the “Happy Birthday” song from beginning to end twice. Rinse your hands well under clean, running water. Dry your hands using a clean towel or air dry them.

See also this TED Talk on how to properly dry your hands with a paper towel. (via a map a day)