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

Bacteria on underwear and socks
After wearing socks all day, they usually have a pungent, sour smell and give the impression of being dirty. This is because feet are one of the parts of the body most prone to sweating. After sweating, bacteria on the skin use the organic matter in the sweat as food, metabolizing it into odor molecules, which naturally make the socks smelly.
Studies have found that worn socks mainly contain sweat, Staphylococcus aureus, fungi, and dead skin cells.
However, if there are no infectious diseases such as athlete's foot, the "dirt" on socks is mostly normal resident bacteria on the skin and their metabolites, which is not very harmful.
As for underwear, in some ways it is indeed much dirtier than socks! Although underwear is worn inside the body, it is in close contact with the reproductive tract and excretory opening. After a day of metabolism, it will retain sweat and secretions, and may even be stained with a little feces! In addition, the humid and warm environment will make it even more prone to bacterial and fungal growth.
Research by American microbiologists has found that an average pair of underwear contains 0.1g of feces, 1,000 parasite cysts, and as many as 10 billion bacteria and viruses, including Salmonella, E. coli, hepatitis A virus, and rotavirus.
So, will washing underwear and socks together cause cross-infection? See the next page!