They are a family of plant pigments (different from flavonoids). Whereas flavonoids take the general strucutre of 2 benzene rings joined by a carbon ring, cartenoids are very large, mostly carbon molecules of varied structure. Cartenoids can be divided into 2 classes: carotenes and xanthophylls. Carotenes typically contain only carbon and hydrogen, and tend to be orange. Xanthophylls have C, H and oxygen atoms on them, and are often yellow.

The best known cartenoid is probably beta-carotene, richly found in carrots and the origin of the class name. Lycopene, which makes the red colour in tomatoes, is also well known. Both of these cartenoids are antioxidants -- they scavange free radical oxygen in the body -- which is thought to slow aging. Studies also suggest that they have anti-cancer properties, although the chemistry of how beta-carotene works may make it less beneficial for heavy smokers. Lycopene is especially recommended to boost fertility in men. Lycopene is more bioavailable in oily processed products like tomato sauces than in the fresh tomato fruit.