Which of the following best describes free radicals?

Free radicals are best described as reactive molecules that can cause damage to cells. They are highly unstable and have unpaired electrons, which makes them seek stability by interacting with other molecules. This reaction can lead to oxidative stress, where healthy cells can be compromised, contributing to aging and various diseases, including cancer. Free radicals are generated naturally in the body during metabolic processes, but external factors like pollution, UV exposure, and smoking can increase their levels. Understanding the role of free radicals is crucial in esthetics, as oxidative stress plays a significant role in skin aging and damage, thus highlighting the importance of antioxidants in skincare.

The other options describe concepts that do not accurately represent free radicals: stable molecules do not contribute to cellular damage, while proteins are involved in immune response, and fatty acids serve functions related to brain health, none of which pertain to the characteristics of free radicals.