Science

How does soap kill germs?

Twenty seconds of scrubbing with soap is one of the best ways to protect yourself — and the people and things you touch — from disease-causing germs. But how exactly do soapy suds kill pathogenic bacteria and viruses that infect us?

Soap’s germ-zapping superpowers are built into its molecular structure: a “head” attached to a long “tail,” according to Dr. Lee Riley, a physician, professor and chair of the Division of Infectious Disease and Vaccinology at the University of California (UC) Berkeley. The head is hydrophilic, or water-loving, while the tail is hydrophobic — water-fearing or water-repelling. That hydrophobic tail has an affinity for fats, and all bacteria and some viruses — including SARS-CoV-2, the coronavirus that causes the disease COVID-19 — have a lipid membrane, which leaves it vulnerable to a soap molecule’s fat-puncturing tail.

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