Washing Their Mouths With Urine
Listerine and Tide Pods did not exist in the past, so people had to look for other ways to clean clothes and get rid of bacteria. They needed to come up with an anti-bacterial solution, so they used something widely available. Human pee contains ammonia and can be sterilized by boiling. While it sounds gross, Bear Grylls himself suggested this when you have nothing else on you.
Tall Hairstyles Were Basically Nests
We are sure that you have seen those high hairstyles during the 18th century. They might seem prim and proper, but they were full of bacteria! They used a mix of real hair and wigs, building them up with lard. The style took a lot of work, so it was common to keep the hair unwashed for weeks on end. As you can imagine, small animals and bugs liked to make themselves at home in the nest-like environment.