Ultraviolet (UV) radiation is part of the electromagnetic spectrum emitted by the sun. UV radiation is categorised as UVA, UVB and UVC rays. Whereas UVC rays (wavelengths of 100-280 nm) are absorbed by the atmospheric ozone, most radiation in the UVA range (315-400 nm) and about 10% of the UVB rays (280-315 nm) reach the Earth’s surface. Both UVA and UVB contribute benefits as well as threats to human health.

Both UVA and UVB cause damage to the skin, age it prematurely, and increase the risk of skin cancer. UVB is the chief culprit behind sunburn, while UVA rays, which penetrate the skin more deeply, are associated with wrinkling, leathering, sagging, and photo-aging. They also exacerbate the carcinogenic effects of UVB rays, and increasingly are being seen as a cause of skin cancer on their own.

Small amounts of UV are essential for the production of vitamin D in people. However, prolonged and over exposure may result in acute and chronic health effects on the skin, eye and immune system.  Sunburn is the best-known acute effect of excessive UV radiation exposure. Over the longer term, UV radiation induces inflammatory reaction of the eye, degenerative changes in cells of the skin, fibrous tissue and blood vessels leading to premature skin aging, photodermatoses and actinic keratoses.  In the most serious cases, skin cancer and cataracts can occur. 

Singapore's UV Index...

UV radiation levels vary substantially with time and place. Singapore, situated at the equator, is consistently in the highest UV Index band. This is why sun safety habits are important for us living in Singapore. 

Sources: http://www.who.int/uv/en/, http://www.skincancer.org/prevention/sun-protection, https://www.thevisioncouncil.org/content/uv-protection/kids