Lycopene is a red pigment found in plants and is part of a large class of plant compounds called carotenoids. Carotenoids are fat soluble and create yellow, orange, or red colors in plants. Carotenoids are not made by humans. Lycopene is not found in high amounts in many plants. The greatest sources of lycopene in fresh fruits and vegetables are watermelon, tomato, red grapefruit, and guava.

Interestingly though, just because a plant or vegetable has a red pigment does not necessarily mean that it contains lycopene. For example, the red color found in strawberries, cherries, etc. is a water soluble pigment called anthocyanin, and is formed by a very different pathway from the carotenoids.

The primary role of carotenoids in plants is to neutralize compounds created during photosynthesis. These compounds are often hydrogen peroxide or singlet oxygen, both of which will attack and destroy cell membranes, ultimately damaging the cell. Singlet oxygen is oxygen with a higher energy charge because outer orbital electrons are spinning in opposite directions.

Humans breathe in oxygen as O2. The biological processes in the body use oxygen for reactions, frequently creating singlet oxygen as a byproduct. The singlet oxygen is very reactive (high electric charge) and therefore must be eliminated by the body before cell damage occurs. The body uses antioxidants, compounds that look for singlet oxygen and neutralizes it. Of the carotenoids, lycopene is the most effective oxygen scavenger because it can neutralize several singlet oxygen with one lycopene molecule. Other antioxidants are Vitamin C (ascorbic acid) and Vitamin E.