<a href=https://explorable.com/cause-and-effect>Establishing Cause and Effect</a>. Cause and effect is one of the most commonly misunderstood concepts in science and is often misused by lawyers, the media, politicians and even scientists themselves, in an attempt to add legitimacy to research.
You can't catch cancer from anyone, in any way. Cancer is not contagious. You can't catch HIV/AIDS just by touching somebody. The AIDS virus is not found in sweat. Yes, you can catch a cold, or the flu by shaking hands with someone if you then put your hands on/near a mucous membrane (eyes, nose, mouth).
Hand washing is the single most important way to prevent the spread of communicable diseases. Use soap, warm water and disposable paper towels. Wash your hands frequently and teach children to wash their hands, too. Hand washing reduces the number of microorganisms on hands that can spread communicable diseases. Open the window to let the fresh air in!