Capsicum is the genus of pepper plants which includes chilli pepper, bell peppers, cayenne and paprika. Most people use the term to refer specifically to bell peppers (red, yellow and green peppers), which do not share the "hot" flavour of their cousins.
Capsicum plants are an excellent source of vitamin C, which is a powerful antioxidant and is known to have a beneficial effect on the immune system and on mood too.
Bell peppers are also extremely rich in carotenoids, including lycopene, beta-carotene, lutein and zeaxanthin. Carotenoids play an important role in maintaining healthy vision and in preventing macular degeneration, and they are also essential antioxidants which help to fight off disease and cellular damage.
Flavonoids such as luteolin, found in peppers, have anti-inflammatory properties, and may help to soothe pain. Peppers are also rich in enzymes which support the role of sulphur in the body, in a way which is known to have health-protective benefits.
Bell peppers are rich in vitamin E, which is essential for good skin health. They also contain the flavonoid quercetin, which has an antihistamine effect and is being studied for its role in helping to prevent heart disease.