The main purpose of sunscreen is to block the sun’s ultraviolet (UV) light from damaging the skin.
UV rays can be split into two classes: UVB rays which are associated with sunburn (think ‘B’ for burn), and UVA rays which are responsible for premature skin aging (think ‘A’ for ageing).
Both types of rays can be responsible for skin cancer.
What is SPF?
All sunscreens have written on the label the Sun Protection Factor, or SPF. The SPF acts as a multiplier. If you apply a sunscreen with SPF 10, you’ll remain protected for 10×10 minutes i.e. 100 minutes.
SPF was introduced in 1962 as a measure of a sunscreen’s protection against UVB – the higher the SPF the greater protection the skin has against sunburn. The star rating shown on sunscreen packaging is an indication of UVA protection – the higher the star rating, the higher the UVA protection.
Tip: Look for ‘broad spectrum’ sunscreen having combined protection from both UVA and UVB rays.
Physical vs chemical sunblocks?
Sunscreens are usually divided into two categories: physical or chemical.
- When applied to the skin, Chemical sunscreens (such as para-aminobenzoic acid, benzophenones, and cinnamates) absorb UV radiation and convert it into harmless forms of energy.
- Physical sunscreens lie on top of the skin and create a physical barrier to UV radiation. Zinc oxide and titanium dioxide are examples of physical sunblocks.
The advantages of physical sunscreens are that they:
- reflect/scatter UV radiation rather than absorb it,
- are not absorbed by the skin and thus provide longer lasting protection
- cause less allergic irritations than chemical sunscreens