Communicable means capable of being spread from one person to another, usually referring to diseases. When you catch a cold from a classmate who sneezed near you, or get the flu from a sick family member, you've contracted a communicable disease. These illnesses spread through germs that travel in the air, on surfaces, or through direct contact.

Just as you communicate ideas through words, communicable diseases spread through bacteria or viruses that move from person to person. Chickenpox, measles, and strep throat are all communicable. Not all illnesses are communicable, though: you can't catch diabetes or a broken bone from someone else, no matter how close you get.

Understanding which diseases are communicable helps explain why schools send sick students home and why doctors tell you to cover your mouth when you cough. These precautions interrupt the chain of transmission. When you wash your hands after being around someone with a communicable illness, you're breaking that chain and protecting yourself and others from getting sick.