What are unstable molecules that can attack the body's cells called?

Unstable molecules that can attack the body's cells are called free radicals.

A free radical is an atom or molecule with at least one unpaired electron, making it unusually reactive. In the body, many are produced naturally during metabolism, especially when mitochondria use oxygen to generate energy. The immune system also uses controlled free-radical reactions to help destroy invading microbes.

The danger comes when free radicals accumulate faster than the body can control them. They may steal electrons from nearby molecules, damaging cell membranes, proteins, and DNA. This chain reaction is often described as oxidative stress. Radiation, tobacco smoke, pollution, inflammation, and some chemical reactions can increase free-radical production.

A common mix-up is treating all free radicals as purely harmful. They also play useful roles in cell signaling, energy chemistry, and immune defense. Antioxidants can neutralize some radicals, but the body’s protection depends on a balanced network of enzymes and molecules rather than on one “miracle” food or supplement.