9. Get Frisky.
Any enjoyable activity (including those between the sheets) that provides stress relief is good for the immune system. Skin-to-skin contact floods the body with oxytocin, a neurotransmitter and hormone that reduces stress responses (like anxiety). Studies have also shown that people who regularly had sex had higher levels of infection-fighting immunoglobulin A (IgA) in their saliva than people who didn’t.