How dirty are socks? Can they be washed with underwear?

When hand washing is the only option

Whether it's the time and force required to wash clothes or the final level of cleanliness, hand washing is far inferior to machine washing.

Studies have found that washing machines using 30°C water and regular detergent for a 45-minute cycle can kill 99 percent of bacteria. In contrast, hand washing is not as effective at eliminating bacteria.