4. Bacteria may build up. During sex, bacteria from the vagina and anus can get into the urethra and multiply, leading to a urinary tract infection. Tip: Pee immediately after the act to flush out bacteria.
5. You burn (some) calories. A study in The New England Journal of Medicine found that a 154-pound person would burn 21 calories during six minutes of sexual activity. So a roll in the sack isn’t as effective as spin class, but a sexy half hour could torch around 100 calories.