保健
ほけん · hoken · JLPT N2 · noun
preservation
🧼 保 (protect) + 健 (healthy) = protecting health, hence hygiene and sanitation
保 means protect or keep, and 健 means healthy or sound. Together they mean keeping health protected, which is why the word covers hygiene and sanitation. 保健室 is the school nurse's office.
保 — person 亻 + 呆 (child/protect phonetic)
Originally an ideograph showing an adult carrying a child on the back, meaning to protect or shield. The right side 呆 evolved from a depiction of a swaddled infant. Over time the meaning broadened from 'protect a child' to 'preserve, guarantee, keep safe.'