UVB (ultraviolet radiation) causes sunburn (and also enables vitamin D production)
UVA causes wrinkles, brown spots (photoageing)
Both UVB and UVA can contribute to the development of skin cancer
SPF = Sun Protection Factor (the number of times longer you can stay in the sun before burning compared to wearing no sunscreen) indicates UVB protection
The amount of UVB radiation that is filtered out varies with different SPFs: - SPF 15 blocks 93% of UVB; - SPF 30 blocks 96.7% of UVB; - SPF 50 blocks 98.3% of UVB.
Always check a product has UVA protection. It is not essential to have the Boots star rating, but if it has, look for 4 or 5 stars. The UVA in a circle is a marker of quality and indicates that the UV protection, specifically the critical wavelength, extends beyond 370nm.
The critical wavelength (CW) is the point at which 90% of the absorption of UV takes place. 370nm is accepted as a minimum standard worldwide.
Water resistant sunscreens are ideal for sports and outdoor activities