A washing-worn skin barrier, and one mosquito bite Two cross-sections. Top: constant washing and sanitizing wear the lipid mortar of the skin barrier thin, and the hands dry out, crack and redden. Bottom: a mosquito's mouthpart reaches a small blood vessel, and any germ in its saliva goes in with it. TWO VIEWS PHASE 1 · HEALTHY INSIDE: CRACKED HANDS OUTSIDE: ONE BITE CROSS-SECTIONS, NOT TO SCALE Lipid “mortar” Washing and sanitizing wear it thin. Crack Hands dry out and crack. Redness The skin underneath reddens. Skin One bite, zoomed in. Germ in the saliva Goes in with the mouthpart. Blood vessel Any germ is carried off in the blood.

Mosquito-borne disease: R&R Lotion, Vector Borne Diseases: Causes, Prevention and Treatment, white paper, pp. 4, 9 and 11. Brick-and-mortar model of the stratum corneum: Elias PM, J Invest Dermatol 1983;80:44s–49s. Illustration for education only.